JUSTICE KIRSHBAUM delivered the Opinion of the Court.

Richard Owen Drake, the defendant, was found guilty by a jury of murder in the first degree, in violation of section 18-3-102, 8B C.R.S. (1986), in connection with the death of his wife, Regina Drake. After further proceedings, the trial court imposed a sentence of death pursuant to section 16-11-103, 8A C.R.S. (1978 1983 Supp.). The defendant has appealed his conviction pursuant to section 16-11-103(7)(a) and C.A.R. 4(e), asserting that numerous errors were committed by the trial court in both the guilt-innocence phase and the sentencing phase of the trial. Although we agree that errors were committed in both phases of the trial, we nevertheless affirm the jury's guilty verdict. However, in view of the nature and extent of the errors affecting the sentencing phase of the trial proceeding, we reverse the sentence imposed by the trial court and order the imposition of the alternative sentence of life imprisonment.

I. THE BASIC FACTS

The following summary of main events puts into an overall perspective the numerous legal issues presented by this appeal. Other pertinent facts will be discussed in the course of addressing those issues.

The defendant and his wife, Regina Drake, had four children during their marriage. The youngest child, a girl, was named Jennifer.

In July of 1982, the defendant purchased a life insurance policy in the face amount of $5,000. Regina was the named insured. The insurer advertised that it would pay all life insurance claims within twenty-four hours. On November 18, 1982, the defendant cancelled a $5,000 life insurance policy that he owned on his life and increased the coverage of the policy covering Regina to $10,000.

During the fall of 1982 the defendant proposed marriage to a co-worker at the bakery where he was employed. He indicated that he would divorce Regina if his proposal were accepted.

On November 24, 1982, Jennifer Drake suddenly died. Both the defendant and Regina experienced great difficulty adjusting to the loss of their daughter. The defendant at times also professed to be upset at what he characterized as Regina's inability to accept Jennifer's death.

In mid-December of 1982, the defendant telephoned his brother James, a resident of Shreveport, Louisiana, asked James to come to Colorado, and mailed him funds to purchase an airline ticket for the trip. James arrived in Grand Junction on December 14, 1982, and met with the defendant that evening. The defendant asked James to kill Regina in return for the anticipated $10,000 proceeds from the life insurance policy on her life. The defendant offered to provide James with a knife and keys to the apartment occupied by the defendant and his family. James agreed.

On December 16, 1982, the defendant left his apartment at about 3:45 a.m. and was driven to his job at the bakery by a friend. At 5:20 a.m., a Grand Junction Police Department operator received a telephone call, later established by police investigation to have been placed by James Drake, indicating that a woman had been stabbed at the defendant's residence. The call was tape recorded and traced to a public telephone located near a local department store. Police officers responding to the call discovered Regina's body, with numerous stab wounds, in the Drake apartment.

At about 6:00 a.m., police officers went to the bakery where the defendant was employed and informed him that Regina had been murdered. During the trial, Sergeant James Hall testified that the defendant immediately threw his helmet to the floor, put his face in his hands and uttered sobbing sounds when advised of his wife's death, but shed no tears. The defendant agreed to accompany the officers to the police station, where he was questioned.

Later that morning James Drake telephoned the defendant's apartment twice, asking to speak to the defendant. At approximately 2:00 that afternoon James Drake phoned the police station, identified himself, said he was calling long distance, and asked to speak to the defendant. The officer answering the call recognized the voice as that of the person who earlier had reported Regina's murder and suspected that the call originated locally. The defendant initially denied that James was in Grand Junction, but subsequently informed the officers that James was staying at a local motel.

The officers went to the motel, found James and, with his consent, searched his room. That search and later investigation of the area near the motel resulted in the discovery of a ski mask, gloves, sales tags from the department store near the telephone booth from which the earlier morning call had been placed, airline boarding passes, a Schrade brand knife with blood stains on it and a matching sheath. James Drake was taken to the police station and was searched. During this search blood stains were found on his shirt, pants and belt and on the ski mask and gloves taken from his motel room.

The defendant was arrested later that day. On December 17, 1982, he was formally charged with murder in the first degree and a defense attorney was appointed to represent him. On February 8, 1983, the defendant tendered a plea of not guilty to the charge. The trial court declined to accept the plea, and no formal plea of not guilty was entered in the case.

On March 28, 1983, the defendant requested a meeting with the Mesa County District Attorney. Investigators Jack Rentfrow and G. Stone of the district attorney's office met briefly with the defendant, but refused to discuss the case unless the defendant waived his attorney's presence. On March 29, at the defendant's request, a second meeting was held with Rentfrow and Stone. The defendant was advised of his rights and signed a form waiving his attorney's presence. An audio tape was made of almost all of that interview, and the defendant signed a written statement that day.

In his March 29 statement the defendant said he arranged for his brother James to visit him in Grand Junction about the death of his daughter Jennifer; that at the meeting the defendant was informed that James had a "contract" to kill five people, including the defendant, Regina, or both, before the end of the year; and that the defendant was told he should either go into business with James or suffer the consequences. The defendant said he told James to go ahead and kill Regina because, in view of her instability over the loss of their daughter, she would not be able to handle his death and he could better care for the remaining children. He stated that he agreed to leave the keys to his apartment in the mailbox in front of his home when he left for work on December 16 and that he gave James a knife. The defendant also stated that at 6:15 a.m. on December 16 he telephoned James and asked that he be killed instead of Regina, but that James said it was too late.

On April 1, the defendant requested another interview with Rentfrow and Stone. After he was given proper advisements, a reduction in the amount of defendant's bond was discussed, but the officials made no promises concerning that matter. The defendant said that he wanted to make another statement and tell the truth. He agreed that this statement could be recorded.

In his April 1 statement, the defendant stated that he called James and said he "needed someone out of the way," paid the cost of James' flight, and met with James on December 14 in Grand Junction. He told James the victim was to be Regina and agreed to pay James $10,000 from life insurance policy proceeds if James would kill Regina. The defendant said he made this arrangement because Regina could not handle Jennifer's death and because he wanted freedom. The defendant stated that on December 15 he and James finalized the plan; that he gave James a knife and left keys to the apartment in the mailbox; and that he did not ask James to abandon the plan.

At trial, which commenced December 5, 1983, the defendant objected to the participation of several prospective jurors on grounds of bias and prejudice. Many of the objections were denied. During the defense portion of the case, the defendant called a clinical psychologist as an expert witness to establish that neither of the two statements made to the investigators was truthful. During the defendant's direct examination of the witness the trial court sustained an objection by the prosecutor to a question seeking to establish the basis of the expert's opinion by reference to discussions between the expert and the defendant. The trial court commented that the expert witness seemed "weird," and interrupted the direct testimony of the witness with comments critical of the defense attorney's performance. The trial court also denied the defendant's request to present testimony from another expert purportedly to the effect that a voice analysis indicated that the defendant's April 1 statement was not true.

After discussions between the defendant's attorney and the trial court, the defendant was advised in the presence of the jury of his right not to testify. He and his attorney indicated that he would nevertheless testify. The defendant told the jury that the April 1 statement was untrue and had been given in the hope of achieving his release from jail. He also testified that he did not participate in any way in Regina's murder.

The jury returned a verdict of guilty, and was then instructed by the trial court concerning the penalty phase of the case. After the introduction of further evidence by the prosecution and the defendant, the jury returned a verdict finding three aggravating factors and no mitigating factors. The trial court imposed a sentence to death, pursuant to section 16-11-103, 8A C.R.S. (1978 1983 Supp.), and this appeal followed.

II. JURY SELECTION PROCEEDINGS A.

The defendant asserts that the trial court's denial of his challenges of certain prospective jurors for cause deprived him of his right to trial by a fair and impartial jury. Although the circumstances surrounding two of these challenges certainly would have supported different results, we conclude that there was no clear abuse of trial court discretion.

A defendant in a criminal proceeding has a fundamental right to a trial by jurors who are fair and impartial; to ensure that right is protected, the trial court must exclude prejudiced or biased persons from the jury. E.g., People v. Abbott, 690 P.2d 1263 (Colo. 1984); People v. Gurule, 628 P.2d 99 (Colo. 1981); Nailor v. People, 200 Colo. 30, 612 P.2d 79 (1980). The trial court must sustain a challenge for cause of a prospective juror if there exists a "state of mind in the juror evincing enmity or bias toward the defendant or the state." § 16-10-103(1)(j), 8A C.R.S. (1986). However, if the court is satisfied that the prospective juror will render an impartial verdict according to the law and the evidence admitted at trial, that person should not be disqualified. Id.; Crim. P. 24(b)(1)(X). Trial courts are afforded broad discretion in ruling on challenges for cause to prospective jurors, and decisions denying such challenges will be set aside only when a clear abuse of discretion is disclosed by the record. Nunez v. People, 737 P.2d 422 (Colo. 1987); People v. Sandoval, 733 P.2d 319 (Colo. 1987); People v. Russo, 713 P.2d 356 (Colo. 1986); People v. Wright, 672 P.2d 518 (Colo. 1983); People v. Taggart, 621 P.2d 1375 (Colo. 1981). This standard recognizes that the trial judge is the only judicial officer able to perform the critical assessments by personal observation of the credibility and demeanor of a prospective juror. E.g., People v. Sandoval, 733 P.2d 319; Nailor v. People, 200 Colo. 30, 612 P.2d 79.

A prospective juror's expression of concern or indication of the presence of some preconceived belief as to some facet of the case does not automatically mandate exclusion of such person for cause. E.g., People v. Sandoval, 733 P.2d 319; People v. Taggart, 621 P.2d 1375; People v. McCrary, 190 Colo. 538, 549 P.2d 1320 (1976). The test to be applied in determining whether a prospective juror should be dismissed for cause is whether the person would be able to set aside any bias or preconceived notion and render an impartial verdict based on the evidence adduced at trial and the instructions given by the court. Nunez v. People, 737 P.2d 422; People v. Vigil, 718 P.2d 496 (Colo. 1986); People v. Abbott, 690 P.2d 1263. The trial court may consider a prospective juror's assurance that he or she can fairly and impartially serve on the case. Nunez v. People, 737 P.2d 422; People v. Sandoval, 733 P.2d 319; People v. Russo, 713 P.2d 356; People v. Wright, 672 P.2d 518.

Here, the defendant challenged three prospective jurors on the ground of bias. The first challenge involved a woman who stated that she was upset because the murder had occurred in the presence of children. This prospective juror gave conflicting statements respecting whether she would be able to follow the trial court's instructions in determining whether aggravating or mitigating circumstances were present. Although the defendant's challenge for cause might well have been sustained, we conclude that, in view of the wide latitude the trial court must be granted in its assessment of credibility and demeanor, its determination that she could set aside her beliefs and apply the court's instructions conscientiously does not constitute an abuse of discretion.

The defendant's second challenge for bias involved a woman who stated that although at the outset she had thought the defendant was guilty, she could set that opinion aside and decide the case on the evidence adduced at trial. The juror indicated that she felt she had reached a neutral position with respect to the defendant's case, but also stated that she had had a relationship with a man who had beaten her and that this personal history might possibly affect her decision-making. Again, we cannot conclude that, on balance, the trial court's refusal to exclude the juror for cause constituted a clear abuse of discretion.

The defendant's third challenge for cause based on bias involved a prospective juror who had talked with some of his co-workers concerning the case. He stated that he could not recall the particulars but that the talk had been "rough," that the defendant would not have a chance if he were judged by this group of workers, and that he "would sure hate to be in [the defense's] shoes." The prospective juror also stated, however, that he himself did not like to prejudge and that he would weigh the facts on their individual merits and follow the trial court's instructions. In view of these statements, the trial court's refusal to excuse this prospective juror for cause did not constitute a clear abuse of discretion.

B.

During jury selection all prospective jurors who were unable to apply the death penalty in any case were excluded. The defendant argues that this practice violated his right under the sixth amendment to the United States Constitution to a fair and impartial jury. We are not persuaded by the defendant's argument.

Here, prospective jurors who indicated that they could not under any circumstances apply the death penalty were, at the request of the prosecutor, excluded for cause by the trial court at the voir dire stage of proceedings. The defendant, relying solely on Grigsby v. Mabry, 758 F.2d 226 (8th Cir. 1985), asserts that such exclusion violated his right to an impartial jury by ensuring that the jury ultimately empanelled was unrepresentative of a cross-section of the community. However, Grigsby v. Mabry was reversed in Lockhart v. McCree, 476 U.S. 162 (1986). In Lockhart, the United States Supreme Court rejected the notion that petit juries must reflect the composition of the community at large and reaffirmed the long-standing rule that the fair cross-section requirement applies only to jury panels or venires. Moreover, the Court observed that even if the fair cross-section requirement were extended to petit juries, the essence of a fair cross-section claim is the systematic exclusion of a "distinctive group," such as racial minorities or women, for reasons entirely unrelated to the ability of individuals within that group to perform the duties of juror in a particular case. Lockhart v. McCree, 106 S. Ct. at 1765, 476 U.S. at ___. Far from being impermissible, exclusion of prospective jurors solely on the basis that they are unable under any circumstances to impose the death penalty serves the state's legitimate interest in having a single jury that can consider the facts impartially and conscientiously apply the law in the case at both the guilt-innocence and sentencing phases of a capital trial. Lockhart v. McCree, 106 S. Ct. at 1768, 476 U.S. at 180, (citing Gregg v. Georgia, 428 U.S. 153 (1976) (joint opinion of Stewart, Powell and Stevens, JJ.); Spaziano v. Florida, 468 U.S. 447 (1984)). We conclude that the defendant's sixth amendment right to trial by a fair and impartial jury was not infringed.

III. THE DETERMINATION OF GUILT

The defendant argues that several evidentiary rulings of the trial court were erroneous and require reversal. He also asserts that the trial court improperly failed to recuse itself because of prejudice against the defendant, acted improperly in advising the defendant in the presence of the jury about the consequences of the defendant's decision to testify, and committed reversible error in failing to enter a formal plea of not guilty in the record of the case. While we conclude that errors were committed, we do not agree that either singly or cumulatively they require reversal of the jury's verdict of guilt.

A.

The defendant contends that the trial court erred in sustaining an objection by the prosecutor to certain portions of the testimony of Dr. Michael Keown, a clinical psychologist called as an expert witness by the defendant. We agree, but conclude that the error was not sufficiently prejudicial to warrant reversal of the defendant's conviction.

At trial, the defendant argued that his brother, James rake, at all times acted independently. Dr. Keown, who had examined the defendant, informed the jury that in his opinion the defendant's March 29 and April 1 statements to investigators Rentfrow and Stone were not reliable because they were the product of a dependent-submissive personality and were designed simply to please his captors. The defendant asked Dr. Keown to tell the jury what statements made to him by the defendant in the course of his interviews supported this opinion. The trial court sustained the prosecutor's objection as hearsay on the basis of CRE 801(c).

Contrary to the trial court's apparent conclusion, the statements made by the defendant to Dr. Keown were not offered into evidence to establish the truth thereof, but rather were offered to establish the basis for Dr. Keown's opinion that the defendant suffered from a dependent-submissive personality disorder. Thus, they did not constitute hearsay evidence under CRE 801(c). Dr. Keown's opinion that neither statement was reliable was consistent with the defendant's theory of the case, and the jury was entitled to evaluate the basis for that opinion. Thus, the trial court erred in sustaining the prosecutor's objection to this proposed testimony.

However, the defendant did not make an offer of proof to the trial court to establish for the record precisely what Dr. Keown would have said, had he been permitted to testify. In the absence thereof, we cannot estimate accurately what prejudice the defendant suffered from the trial court's erroneous ruling. The jury was informed of Dr. Keown's opinion. Furthermore, the defendant's own testimony supported the theory that neither of his two statements was believable. In view of these facts, and considering the weight of all the evidence indicating the defendant's guilt, we do not find the trial court's error sufficiently prejudicial to require reversal.

B.

The defendant contends that the trial court erred in sustaining an objection by the prosecutor to proposed cross-examination by defense counsel of Carrie Buller, a prosecution witness who had worked with the defendant at the bakery. On direct examination, Buller testified that in late 1982 the defendant asked her to marry him, gave her a bracelet, and told her he intended to divorce Regina. On cross-examination, the defendant asked Buller if she had ever been convicted of an offense. The prosecutor objected, the jury was excused, and the prosecutor argued that although Buller had sustained a federal conviction, the offense was a misdemeanor rather than a felony, and therefore the fact of the conviction was not admissible for purposes of impeachment. The defendant's attorney, who had represented Buller in the federal court proceedings, argued that because the conviction was for fraudulent conduct it was admissible. Stating that "truthfulness is not an issue at this point," the trial court sustained the objection.

The trial court's comment was inaccurate; the truthfulness of any witness is always a potential issue at trial. It is generally true that the fact of a prior felony conviction is admissible as impeachment evidence, but that evidence of a prior misdemeanor conviction is not. § 13-90-101, 6A C.R.S. (1987); People v. Robles, 183 Colo. 4, 514 P.2d 630 (1973). In some situations, however, such as when a party seeks to establish that a witness habitually utters untrue statements, the circumstances surrounding a misdemeanor conviction may be disclosed to a jury. CRE 608(b); see People v. Mejia, 188 Colo. 120, 534 P.2d 779 (1975); People v. Armstrong, 704 P.2d 877 (Colo.App. 1985).

Here, the defendant did not suggest that he wished to explore the circumstances surrounding Buller's federal conviction; he indicated only that he wished to inform the jury of the fact of the conviction. The defendant did not suggest that the fact of the conviction would controvert any specific testimony given by Buller — another recognized exception to the prohibition of admission of evidence of a misdemeanor conviction for general impeachment purposes. See People v. Sasson, 628 P.2d 120 (Colo.App. 1980); People v. Terranova, 38 Colo. App. 476, 563 P.2d 363 (1976). Under these circumstances, the trial court did not abuse its discretion in sustaining the prosecution's objection to the defendant's question, although the trial court's stated reason for its ruling was inaccurate.

The defendant also argues on appeal that he was denied effective assistance of counsel, in violation of the sixth amendment to the United States Constitution, because his defense attorney's representation of Buller during her federal trial created a conflict of interest that improperly restricted his ability to cross-examine her concerning the circumstances of that conviction. We find no basis in the record to support the assumption that defendant's attorney did not fully explore the circumstances of Buller's conviction because of conflict of interest concerns. To the contrary, the public record of that conviction contained ample information to illustrate the circumstances thereof without resort to any information that might have been privileged. See Cuyler v. Sullivan, 446 U.S. 335 (1980); United States v. Davis, 766 F.2d 1452 (10th Cir.), cert. denied, 474 U.S. 908 (1985).

C.

The defendant argues that the trial court erroneously sustained the prosecutor's objection to testimony of Dr. Henry Truby, a linguistics specialist familiar with voiceprint analysis. Although Dr. Truby had never examined the defendant, he had examined tape recordings of the defendant's March 29 and April 1 statements. The prosecutor objected to the admission of this testimony on the ground that the practice of voiceprint analysis constituted too speculative a field of inquiry to permit opinion testimony based thereon, and on the further ground that the testimony would not assist the jury. In response, the defendant made an offer of proof establishing that Dr. Truby would testify that, according to his analysis, the defendant's inflection, intonation, speech patterns and other characteristics, as revealed by the tape recordings, were substantially similar on both occasions; and that, therefore, either both statements were accurate or both statements were false, in direct contradiction to the prosecution's theory that the March 29 statement was false and the April 1 statement was true. The defendant intended to rely on Dr. Truby's testimony to corroborate the opinion of Dr. Keown that both statements were unreliable because they were simply products of the defendant's dependent-submissive personality syndrome. The trial court stated that Dr. Truby's opinion "would only confuse the jury and it would add nothing of a material relevance . . . for all practical purposes."

The trial court's conclusion that Dr. Truby's testimony was not relevant to material issues in the case is incorrect. For purposes of admissibility, evidence "having any tendency to make the existence of any fact that is of consequence to the determination of the action more probable or less probable than it would have been without the evidence" is material evidence. CRE 401. Dr. Truby's testimony was relevant to the defendant's position that neither of his statements was reliable.

At trial, however, the prosecutor argued in effect that the discipline of voice analysis is in its infancy and that Dr. Truby's field of expertise was not recognized as a sufficiently established discipline in the scientific community to permit the jury to consider his opinion testimony. The accuracy of voice analysis techniques has been challenged by several clinical studies. See A. Moenssens F. Inbau, Scientific Evidence in Criminal Cases, 648-51 (2d ed. 1978). Many courts have refused to admit voice analysis evidence on the ground that voice analysis techniques contain the same inherent deficiencies that have led, in general, to rejection of polygraph test results as evidence in judicial proceedings. See People v. Anderson, 637 P.2d 354 (Colo. 1981); see also Barrel of Fun, Inc. v. State Farm Fire Casualty Co., 739 F.2d 1028 (5th Cir. 1984); United States v. Traficant, 566 F. Supp. 1046 (N.D. Ohio 1983); Neises v. Solomon State Bank, 236 Kan. 767, 696 P.2d 372 (1985); State v. Schouest, 351 So.2d 462 (La. 1977); Smith v. State, 31 Md. App. 106, 355 A.2d 527 (1976); State v. Ochalla, 285 N.W.2d 683 (Minn. 1979); People v. Tarsia, 50 N.Y.2d 1, 427 N.Y.S.2d 944, 405 N.E.2d 188 (1980); State v. Makerson, 52 N.C. App. 149, 277 S.E.2d 869 (1981); Sabag v. Continental South Dakota, 374 N.W.2d 349 (S.D. 1985); but cf. Simon Neustadt Family Center, Inc. v. Bludworth, 97 N.M. 500, 641 P.2d 531 (1982). We agree with this line of decisions. Therefore, in view of the prosecution's objection, the defendant's failure to establish that the technique used by Dr. Truby was sufficiently reliable to support his proposed opinions concerning the defendant's statements justified the trial court's decision to sustain the objection.

D.

The defendant argues that the trial court erred in failing to excise certain portions of the tape recording of the April 1 statement; in admitting into evidence certain color slides used by the pathologist who performed the autopsy on Regina; and in failing to maintain a position of impartiality throughout the trial. He asserts these errors, singly or cumulatively, require reversal of his conviction. We disagree.

The defendant did not object at trial to the conduct here challenged. Therefore, this conduct will be viewed in light of the plain error standard. Wilson v. People, 743 P.2d 415 (Colo. 1987); People v. Barker, 180 Colo. 28, 501 P.2d 1041 (1972); see Crim. P. 52(b).

A tape recording of the defendant's April 1 statement was played to the jury. The defendant asserts that references during the interview to other criminal conduct by the defendant and to whether he may have had any intent to kill his children, although not objected to at trial, should have been deleted from the tape under our decision in Callis v. People, 692 P.2d 1045 (Colo. 1984).

In McRae v. People, 131 Colo. 305, 281 P.2d 153 (1955), this court concluded that when a statement made by a defendant is admitted in a criminal case the entire statement is admissible. In Callis, we rejected this rule, holding that evidence of prior criminality not otherwise relevant and admissible should not be introduced even though part of a defendant's otherwise admissible statement. Callis, however, was expressly made applicable only to cases filed after the effective date of that decision. Under the rule announced in McRae, which governed this trial, no error was committed.

This court has frequently noted that photographs relevant to issues in a criminal case are not rendered inadmissible because their content reveals grim details that might shock or otherwise upset the trier of fact. People v. Mattas, 645 P.2d 254 (Colo. 1982); People v. Steele, 193 Colo. 87, 563 P.2d 6 (1977); People v. Hosier, 186 Colo. 116, 525 P.2d 1161 (1974). The color slides to which the defendant refers were relevant to the pathologist's opinions concerning the cause of Regina's death. The trial court did not commit plain error in admitting these slides into evidence in the absence of any objection thereto.

The defendant refers to several comments made by the trial judge during the course of the trial which, when coupled with what the defendant asserts was frequent use of a snide and insinuating manner directed toward the defendant, defense counsel and defense witnesses, evidenced such prejudice and animosity against the defendant that the trial court should have voluntarily recused itself from these proceedings. Colorado Rule of Criminal Procedure 21(b)(2) provides that "[a]ny judge who knows of circumstances which disqualify him in a case shall, on his own motion, disqualify himself."

The parties in a criminal case are entitled to a trial presided over by a judge free of any bias, prejudice or interest directed toward any party or witness. A defendant asserting bias on the part of a trial judge must establish that the judge had a substantial bent of mind against him or her. See People v. Botham, 629 P.2d 589, 595 (Colo. 1981); Carr v. Barnes, 196 Colo. 70, 74, 580 P.2d 803, 805 (1978). The record must establish such bias clearly; mere speculative statements and conclusions are insufficient to satisfy the burden of proof. Carr v. Barnes, 196 Colo. 70, 580 P.2d 803; Walker v. People, 126 Colo. 135, 248 P.2d 287 (1952).

The record in this case discloses several incidents in which the trial court made disparaging remarks to defense counsel concerning questions propounded to witnesses. When informed that the defendant's children were potential witnesses, the trial court stated, in the presence of the jury, "I seriously hope that Mr. Drake will seriously consider any further involvement of his children in this affair. However, I don't want to be understood as indicating what I think he ought to do in his own defense. . . ." The trial court frequently interrupted the defendant's examination of witnesses, including the direct examination of a psychologist called by the defendant. When the defense counsel at one point attempted to clarify for the trial court a complex point regarding the basis of an expert witness' opinion concerning the defendant's asserted personality disorder, the trial court told the defense attorney, "You will listen to what he has to say and you will keep quiet." Additionally, when the prosecutor's objection to the proposed testimony of Dr. Truby, a voice analyst, was initially sustained, the trial court indicated that such testimony might be admissible depending upon the contents of the defendant's testimony, but then, after the defendant testified, again sustained the prosecution's objection to the testimony.

It is not possible to capture from a reading of the record a full appreciation of intonations and gestures that may well significantly shape the effect of comments made by the trial court during a trial. When a trial attorney perceives conduct that appears to evidence bias, prejudice or interest, the attorney should of course state such perceptions on the record. The record in this case does reveal incidents of trial court comments to defense counsel that were rude, and some discussions with defense witnesses that evidenced irritation. Such comments and discussions should be avoided, especially when uttered in the presence of the jury. We cannot say, however, that the record as a whole establishes that bent of mind against the defendant or his attorney that warrants a finding of bias, prejudice or interest against the defendant. We therefore reject this argument. We are also satisfied that, when viewed cumulatively and in light of the record as a whole, the errors that were made by the trial court in its conduct of the trial do not constitute plain error warranting reversal of the defendant's conviction.

E.

The defendant asserts that the trial court failed to advise him properly of the consequences of any decision to testify at trial. He specifically claims that the trial court erred in conducting the advisement in the presence of the jury, in failing to warn the defendant that he could be cross-examined concerning prior convictions, in failing to inform the defendant that if he elected not to testify the jury could be informed of that election and in failing to state that any decision to testify or not to testify was a decision ultimately to be made by the defendant himself.

In People v. Curtis, 681 P.2d 504 (Colo. 1984), we strongly recommended that any advisement of the right not to testify should be performed outside the presence of the jury. Because it is not possible to predict what questions, explanations and discussions might occur during such an advisement, there is inherent danger of prejudice to the defendant in permitting the jury to be present. Furthermore, it is also extremely difficult to measure the extent of any prejudice occurring in such circumstances. We again strongly caution that any such advisement should be conducted outside the presence of the jury.

While there is always a danger that a defendant might feel coerced into testifying when the trial court's advisement of the right to remain silent is conducted in the presence of the jury, nothing in this record indicates such factor is present in this case. In view of the defendant's decision to testify, and considering the weight of the evidence establishing his guilt, we find the trial court's error to be harmless beyond a reasonable doubt. See Crim. P. 52(a).

In any case challenging the validity of a waiver of the right not to testify, the reviewing court must determine whether the defendant in fact knowingly and intelligently waived this fundamental right. People v. Mozee, 723 P.2d 117 (Colo. 1986); Reed v. People, 171 Colo. 421, 467 P.2d 809 (1970). In Mozee, we observed that an advisement of the nature and consequences of the right to testify to a defendant who chooses not to testify differs materially from an advisement of the right to remain silent to a defendant who elects to testify. We noted that defense counsel has a responsibility to advise the defendant of matters associated with the right to remain silent, and that on several occasions between arrest and trial the defendant is apprised of this fundamental right by law enforcement and judicial officials. In this case, the defendant stated that he had been advised of his right not to testify by his attorney. The defendant's trial counsel also indicated on the record that he as well as the trial court had made inquiries of the defendant prior to the formal advisement now challenged. In view of these circumstances, we conclude that the defendant's waiver of the right to remain silent was effective.

F.

The defendant contends that the trial court erred in failing to insist sua sponte upon the entry of a formal not guilty plea and in failing to sua sponte take steps to mitigate the effect of an allegedly improper question asked by the prosecutor during the cross-examination of the defendant. We do not agree.

1.

When the defendant initially tendered a plea of not guilty on February 8, 1983, the trial court rejected the plea pending determination of several motions the defendant filed. The plea was not tendered again and, without objection, no formal plea of not guilty was ever entered in the case.

Section 16-7-208, 8A C.R.S. (1987), provides that if no plea is entered in a criminal case, "the case shall for all purposes be considered as one in which a plea of not guilty has been entered." Similarly, section 16-7-203, 8A C.R.S. (1987), provides that irregularities in an arraignment not affecting substantial rights of a defendant and not objected to shall not "affect the validity of any proceeding in the cause." These statutes, while recognizing fully a defendant's right to respond in whatever manner the defendant elects to any criminal charge, are designed to ensure that convictions may not be overturned because of irregularities in arraignment proceedings. Here, there was never any question about the defendant's position, stated on the record on February 8, 1983, and never altered, that he was not guilty of the charged offense. In view of the purpose of these statutory provisions and the lack of any prejudice to the defendant from this procedural irregularity, we find no basis for reversal of the defendant's conviction in this unusual circumstance. See Landford v. People, 148 Colo. 300, 365 P.2d 893 (1961), cert. denied, 369 U.S. 862 (1962).

2.

During cross-examination of the defendant by the prosecutor, in response to a prosecutor's question about any prior felony conviction, the defendant said he had been convicted of two felonies. When the prosecutor asked, "What are they?", the defendant said one was for extortion and one was for burglary. No objection was interposed to the prosecutor's question. However, defense counsel later informed the trial court that the extortion case had in fact been a juvenile proceeding; no further reference was made by the prosecutor to the extortion matter. The defendant now urges reversal because of the prosecutor's question, apparently on the theory that the trial court had some duty to take some step once the issue had been raised.

The credibility of a defendant who testifies in a criminal case is subject to impeachment by good faith reference by the prosecutor to prior felony convictions. People v. Thompson, 182 Colo. 198, 200, 511 P.2d 909, 910 (1973). However, a juvenile proceeding is not a criminal proceeding, and a prior adjudication of delinquency cannot be used for such impeachment purposes. See People v. Apodaca, 668 P.2d 941 (Colo.App. 1982), aff'd in part, rev'd on other grounds, 712 P.2d 467 (Colo. 1985). In the absence of an objection, a lack of good faith will not be presumed on appeal, and a defendant seeking to reverse a conviction because of improper prosecutorial inquiry into prior criminal conduct must demonstrate prejudice. People v. Ciari, 189 Colo. 325, 328-29, 540 P.2d 1094, 1097 (1975); People v. Lewis, 180 Colo. 423, 426-27, 506 P.2d 125, 126-27 (1973). The record here does not support the defendant's assertion that, in light of the prosecutor's knowledge of the defendant's criminal record, the question "What are they?" was proposed in bad faith. Nor does the record suggest that the defendant's isolated voluntary reference to this juvenile adjudication resulted in substantial prejudice to him. In the absence of any request by the defendant, the trial court had no duty to comment on this issue to the jury. We, therefore, reject this argument.

IV. SPEEDY TRIAL

The defendant argues that his right to speedy trial, as established by section 18-1-405, 8B C.R.S. (1986), and Crim. P. 48(b), was denied in this case. Acknowledging that he at no time requested the trial court to dismiss the case on lack of speedy trial grounds, he argues that his silence should not be deemed a waiver of the right. He further contends that the failure of the trial court to enter a formal plea of not guilty during the trial makes calculation of the date from which the speedy trial period began to run impossible and excuses his failure to assert any objection. The argument is without merit.

Section 18-1-405(5), 8 C.R.S. (1978), in effect during the trial, contained the following pertinent provisions:

"To be entitled to a dismissal under subsection (1) of this section, the defendant must move for dismissal prior to the commencement of his trial. . . . Failure to so move is a waiver of the defendant's rights under this section."

This language, as well as the almost identical language of Crim. P. 48(b)(5), specifically provides that the failure to move for dismissal prior to the beginning of the trial is itself a waiver of the statutory right. We have previously noted that the trial court's failure to enter a formal not guilty plea must be treated as if such plea had been entered. Certainly the date from which the defendant's right to speedy trial began to run in this case could be fixed no earlier than February 8, 1983. Whatever date might be selected as initiating the speedy trial period, the defendant's failure to timely assert some objection to the proceeding based on speedy trial considerations constituted a waiver of that right.

V. SENTENCING PROCEEDINGS

The defendant contends that the death sentence imposed by the trial court must be reversed due to the trial court's failure to instruct the jury in unambiguous terms that the jury's verdicts with respect to the presence or absence of mitigating and aggravating factors would be the sole determinants of whether the defendant would be sentenced to life imprisonment or to death. We agree.

Pursuant to the sentencing statute applicable to this case, section 16-11-103, 8 C.R.S. (1978 1983 Supp.), when a jury verdict of guilty is returned in a class 1 felony case, the trial court must conduct a sentencing hearing to determine whether the defendant should be sentenced to life imprisonment or to death.

Under this provision, the jury that determined the defendant's guilt must also return special verdicts concerning the presence or absence of

statutorily defined mitigating, additional mitigating and aggravating factors regarding the offender and the circumstances surrounding the offense. If the jury finds the presence of one or more mitigating or additional mitigating factors, or finds the absence of aggravating factors, the trial court must sentence the defendant to life imprisonment. If the jury finds an absence of any mitigating or additional mitigating factors and also finds the presence of at least one aggravating factor, the court must sentence the defendant to death.

In People v. Durre, 690 P.2d 165 (Colo. 1984), this court concluded that under the provisions of section 16-11-103, 8 C.R.S. (1978 1983 Supp.), a death sentence imposed by a trial court must be reversed where the jury that returned verdicts on mitigating and aggravating circumstances was not adequately informed of the effect of such verdicts on the ultimate question of life imprisonment or death. Although the trial court in Durre orally advised the jurors at the outset of the sentencing hearing that their decision as to the existence of mitigating and aggravating factors would "determine what penalty should be imposed," the trial court did not inform the jurors of the effect of their verdicts on the life or death of the defendant. Id. at 174 n. 15. We recognized that a verdict form which required the jury to determine whether there were additional mitigating factors sufficient to justify life imprisonment might well be interpreted as merely vesting the jury with an advisory role, with the trial court retaining discretion respecting the imposition of penalty. People v. Durre, 690 P.2d at 174. We held:

"[I]n order to eliminate any uncertainty on the part of jurors regarding the effect of their verdicts on the issue of punishment, trial courts at the conclusion of the evidentiary stage of a capital sentencing hearing must inform the jury by an appropriate instruction that verdicts of no mitigating and no additional mitigating circumstances and a verdict of one or more aggravating circumstances necessarily require the imposition of a death sentence; that a verdict of mitigating or additional mitigating circumstances, or a verdict of no aggravating circumstances, necessarily requires the imposition of a sentence to life imprisonment; and that under no circumstances does the court have any discretion on the matter of penalty."

People v. Durre, 690 P.2d at 174 (footnote omitted).

We acknowledged in Durre the well established requirements that a criminal jury must express its decision in terms devoid of ambiguity, People v. Durre, 690 P.2d at 173 (citing Yeager v. People, 170 Colo. 405, 462 P.2d 487 (1969)), and that a criminal verdict must "convey beyond a reasonable doubt the meaning and intention of the jury," People v. Durre, 690 P.2d at 173 (quoting Yeager v. People, 170 Colo. at 410, 462 P.2d at 489, and citing Kreiser v. People, 199 Colo. 20, 604 P.2d 27 (1979); Johnson v. People, 174 Colo. 75, 482 P.2d 105 (1971)). Our holding was grounded firmly upon the need to ensure certainty and reliability in a criminal verdict, a need implicit in the reasonable doubt standard, and upon the enhanced need for certainty and reliability in imposing the appropriate punishment in a capital case, requiring careful scrutiny by virtue of the unique severity and irrevocability of the permissible punishment. People v. Durre, 690 P.2d at 173 (citing Zant v. Stephens, 462 U.S. 862 (1983); California v. Ramos, 463 U.S. 992 (1983); Eddings v. Oklahoma, 455 U.S. 104 (1982); Lockett v. Ohio, 438 U.S. 586 (1978) (plurality opinion); Woodson v. North Carolina, 428 U.S. 280 (1976) (plurality opinion)). We noted as well that the General Assembly, by mandating unanimity in jury verdicts, had recognized the need for certainty and reliability in the jury's decision in criminal trials in general and in capital sentencing verdicts in particular. People v. Durre, 690 P.2d at 173 (citing § 16-11-103(4), 8 C.R.S. (1978 1983 Supp.)).

In this case, the trial court gave no advisement respecting the jury's role at the commencement of the sentencing hearing. At the conclusion of the sentencing hearing the trial court gave the following critical instructions to the jury:

"INSTRUCTION NO. 2

"The Defendant in this case has been found guilty of the offense of murder in the first degree. It is now your duty to make a finding of whether mitigating circumstances exist and if not, whether aggravating circumstances have been proven beyond a reasonable doubt. In arriving at this determination, you should consider all of the evidence presented at the trial and sentencing hearing.

"In determining if mitigating factors exist, consider the following:

"(1) The Defendant was under the age of eighteen; or

"(2) His capacity to appreciate the wrongfulness of his conduct or to conform his conduct to the requirements of law was significantly impaired, but not so impaired as to constitute a defense to prosecution; or,

"(3) He was under unusual and substantial duress, although not such duress as to constitute a defense to prosecution; or

"(4) He was a principal in the offense, which was committed by another, but his participation was relatively minor, although not so minor as to constitute a defense to prosecution; or,

"(5) He could not reasonably have foreseen that his conduct in the course of the commission of the offense for which he was convicted would cause, or would create a grave risk of causing, death to another person;

"(6) Additionally, you may consider the following: the emotional state of the Defendant at the time the crime was committed; the absence of any significant prior convictions; the extent of the Defendant's cooperation with law enforcement officers or agencies and with the office of the prosecuting district attorney; the influence of drugs or alcohol; the good faith, although mistaken, belief by the Defendant that circumstances existed which constituted a moral justification for the Defendant's conduct; the age of the Defendant at the time of the commission of the crime; and whether any other relevant evidence bearing on the question of mitigation exists to justify the sentence of life imprisonment.

"Should you find, however, that none of the above mitigating factors exist, you shall determine if the People have proven any aggravating factor beyond a reasonable doubt. Therefore, consider if:

"(1) The Defendant has been a party to an agreement to kill another person in furtherance of which a person has been intentionally killed; or

"(2) In the commission of the offense, the Defendant knowingly created a grave risk of death to another person in addition to the victim of the offense; or

"(3) He committed the offense in an especially heinous, cruel or depraved manner.

. . . .

"INSTRUCTION NO. 4

"You are instructed that you do not necessarily have to find the existence of either mitigating or aggravating circumstances in this case, and if you so determine, the foreman should sign the verdict form without checking any of the boxes."

These instructions, substantially similar to those given in Durre, did not inform the jury that the decision respecting aggravating and mitigating circumstances necessarily determined whether the penalty imposed would be life imprisonment or death. While Instruction No. 2 advised the jury to consider whether there was evidence of additional mitigating factors to justify a sentence of life imprisonment, it failed to inform the jury of the effect of its verdicts. Like the instructions in Durre, these directions tended to obscure the fact that, unlike other sentencing procedures under the Colorado Criminal Code, the jury and only the jury had the authority and responsibility to determine which of two possible sentences would be imposed upon the defendant.

The verdict form submitted to the jury, similar to that submitted in Durre, stated as follows:

"We, the Jury, having considered all of the evidence, find the existence of one or more of the following mitigating factors:

"( ) A. The Defendant was under the age of eighteen; or

"( ) B. His capacity to appreciate the wrongfulness of his conduct or to conform his conduct to the requirements of law was significantly impaired, but not so impaired as to constitute a defense to prosecution; or,

"( ) C. He was under unusual and substantial duress, although not such duress as to constitute a defense to prosecution; or

"( ) D. He was a principal in the offense, which was committed by another, but his participation was relatively minor, although not so minor as to constitute a defense to prosecution; or,

"( ) E. He could not reasonably have foreseen that his conduct in the course of the commission of the offense for which he was convicted would cause, or would create a grave risk of causing, death to another person.

"IF YOU CHECK ANY OF THE FOREGOING, YOU NEED NOT PROCEED FURTHER, BUT IF NONE OF THE BOXES ARE CHECKED, YOU MUST PROCEED TO THE FOLLOWING SET OF CIRCUMSTANCES. YOU NEED NOT CHECK ANY OF THE FOLLOWING BOXES, BUT IF YOU FIND ONE OR MORE OF THE FOLLOWING CIRCUMSTANCES, THE APPROPRIATE BOX SHOULD BE CHECKED.

"We, the Jury, having considered all of the evidence, find one or more aggravating factors:

"( ) A. The Defendant has been a party to an agreement to kill another person in furtherance of which a person has been intentionally killed; or,

"( ) B. In the commission of the offense, the Defendant knowingly created a grave risk of death to another person in addition to the victim of the offense; or,

"( ) C. The Defendant committed the offense in an especially heinous, cruel or depraved manner.

"IF YOU CHECK ANY OF THE ABOVE AGGRAVATING FACTORS, YOU MUST PROCEED TO CONSIDER ANY OTHER MITIGATING FACTORS. YOU MAY CONSIDER ANY FACT INCLUDING BUT NOT LIMITED TO THE FOLLOWING, IN DECIDING WHETHER A SENTENCE OF LIFE IMPRISONMENT RATHER THAN DEATH IS JUSTIFIED:

"We, the Jury, having considered all of the evidence, find one or more mitigating factors justifies the sentence of life imprisonment rather than death:

"( ) A. The emotional state of the Defendant at the time the crime was committed;

"( ) B. The absence of any significant prior conviction of the Defendant;

"( ) C. The extent of the Defendant's cooperation with law enforcement officers or agencies, and with the office of the prosecuting district attorney;

"( ) D. The influence of alcohol or drugs;

"( ) E. The good faith, though mistaken belief by the Defendant that circumstances existed which constituted a moral justification for the Defendant's conduct;

"( ) F. The age of the Defendant at the time of the commission of the crime;

"( ) G. The Defendant is not a continuing threat to society;

"( ) H. Any other factor which bears on the question of mitigation."

The jury here found none of the first set of mitigating factors present, found all three of the aggravating factors present and found present none of the additional mitigating factors which might justify a sentence of life imprisonment. The verdict form, however, did not advise the jury that its verdicts constituted more than a mere recommendation in sentencing with discretion in the trial court to accept the jury's conclusion. In so critical an area, the instructions and verdict forms must inform the jury of its ultimate role in unambiguous terms.

Section 16-11-103 reposes no discretion in the trial court respecting the imposition of sentence. People v. Durre, 690 P.2d at 171. While there is no constitutional right to sentencing by a jury in a capital proceeding, Spaziano v. Florida, 468 U.S. 447, 457-65 (1984), the sentencing authority, whether it be judge or jury, must at a minimum weigh any aggravating and mitigating factors present and consciously decide whether, in light of those factors, a sentence of death is the appropriate sentence for that particular offender, see, e.g., id.; Zant v. Stephens, 462 U.S. 862, 890; Eddings v. Oklahoma, 455 U.S. 104; Lockett v. Ohio, 438 U.S. 586 (plurality opinion); Gregg v. Georgia, 428 U.S. 153 (1976); Jurek v. Texas, 428 U.S. 262 (1976) (joint opinion of Stewart, Powell, and Stevens, JJ.); Woodson v. North Carolina, 428 U.S. 280 (plurality opinion). Because the sentencing authority, in this case the jury, was not clearly and unambiguously apprised by any instructions or by jury verdict forms of its role as the sole arbiter of whether a sentence of death should be imposed upon the defendant, we find inescapable the conclusion that doubt or speculation exists as to whether "death is the appropriate punishment in [this] specific case." Woodson v. North Carolina, 428 U.S. at 305 (plurality opinion). See also State v. Ramseur, 106 N.J. 123, 524 A.2d 188 (1987) (death sentence reversed where trial court's instructions may have left jury with impression it was not responsible for deciding defendant's sentence).

Relying on Caldwell v. Mississippi, 472 U.S. 320 (1985), the defendant also argues that certain comments made by the prosecutor so diminished the jury's sense of responsibility that reversal of his death sentence is mandated. In Caldwell, defense counsel, in closing argument at a capital sentencing proceeding, asked the jury to show mercy and emphasized the gravity and awesomeness of the jury's responsibility in deciding whether to impose a death sentence. In response, the prosecutor argued, "Now, [the attorneys for the defense] would have you believe that you're going to kill this man and they know — they know that your decision is not the final decision. My God, how unfair can you be? Your job is reviewable. They know it." Overruling an objection by defense counsel, the trial court stated, "I think it proper that the jury realize that it is reviewable automatically as the death penalty commands." The prosecutor then added, "[T]he decision you render is automatically reviewable by the Supreme Court." The United States Supreme Court vacated the death sentence, holding that the need for reliability in the imposition of a death sentence mandated the conclusion that "it is constitutionally impermissible to rest a death sentence on a determination made by a sentencer who has been led to believe that the responsibility for determining the appropriateness of the defendant's death rests elsewhere." Caldwell v. Mississippi, 472 U.S. at 328-30.

Here, the prosecutor made the following comments during closing argument at the sentencing proceeding:

"I just would remind you that it is a shared responsibility that you have. This does not just fly out of anywhere and you suddenly have to decide that without any guidelines as to what to do and what not to do. This is a law that was passed here in our state and this case has come up through the system and has been looked at and obviously it has gone through this Court. You have made a determination of guilty and now at this particular stage of the proceedings, you are to make a factual determination based on the evidence here and where it goes from there, I will not elaborate. I am not trying to minimize the responsibility that you have but I would remind you that it is a shared responsibility and that is our law here in the State of Colorado.

. . . .

"Now, [defense counsel] has told you that the death penalty is final. Indeed it is but what happened to Regina is also final. There is no coming back from that. There is no appeal from that.

. . . .

"I would again like to remind you that what you have is a shared responsibility. This is the law in our state that was passed. You are not alone. This case would not be here but for the actions of the police and it would not be here but for the actions of the prosecution and we are asking for this in your findings of fact and as you were told during the voir dire, you do not directly administer this. That job goes to the Court and you are part of the process and don't let anybody use your decency against you to say that you did it, but who did it?"

These comments are, of course, susceptible of several interpretations. Thus, it is highly likely that these remarks injected an element of confusion for the jury. Without clarification from the trial court, they may well have resulted in a diminution of the jury's sense of responsibility for the ultimate imposition of sentence at the critical stage in the proceedings when consideration of the appropriate punishment was the task immediately at hand. E.g. People v. Perez, 108 Ill.2d 70, 483 N.E.2d 250 (1985) (although trial judge and prosecutor mentioned that jury would "recommend" whether to impose death penalty, no reversible error where trial judge properly instructed jury that the court had no discretion regarding sentencing), cert. denied, 474 U.S. 1110 (1986); State v. Clark, 492 So.2d 862 (La. 1986) (death sentence set aside because of prosecutor's lengthy reference to automatic appellate review of death sentences); Commonwealth v. Baker, 511 Pa. 1, 511 A.2d 777 (1986) (death sentence reversed where prosecutor's comments during penalty phase concerning "appeal after appeal after appeal" tended to minimize jury's sense of responsibility); State v. South, 285 S.C. 529, 331 S.E.2d 775 (death sentence upheld on the basis that trial court's instructions and defense counsel's arguments adequately dealt with prosecutor's improper comment that there were safeguards in the system which he could not discuss), cert. denied, 474 U.S. 888 (1985); see also Frye v. Commonwealth, 231 Va. 370, 345 S.E.2d 267 (1986) (comments of prosecutor and trial judge that jury's verdict was mere recommendation required reversal of death sentence where statute referred to jury's verdict as a recommendation but also provided that only upon good cause shown could trial court set aside a jury verdict of death and impose lesser penalty of life imprisonment). We must conclude that such comments, by implying that the jury had only an indirect or advisory role rather than the ultimate role in the imposition of sentence, were improper and, although not dispositive, constitute an additional factor casting doubt upon the reliability of the sentence in this case. In view of all these circumstances, the absence of unambiguous instructions and adequate verdict forms clearly advising the jury of its absolute responsibility in determining the sentence to be imposed requires reversal of the sentence to death entered by the trial court.

VI. CONCLUSION

In view of the necessity of reversing the sentence to death, we should not and do not reach the defendant's arguments that certain portions of section 16-11-103 violate constitutional standards. The judgment of conviction is affirmed, the judgment of sentence to death is reversed and the case is remanded to the trial court with directions to enter the alternatively authorized sentence of life imprisonment.

Justice Erickson specially concurs. Justice Rovira and Justice Vollack concur in part and dissent in part.