EUGENE A. WRIGHT, Circuit Judge:

In April 1988 Quinton Boise, a six-week-old baby, died on the Warm Springs Indian Reservation. Following an investigation, the government charged his father, Earl Boise, with second degree murder in violation of 18 U.S.C. § 1111, 1153. A jury found him guilty and the court sentenced him to 240 months of imprisonment.

I. Sufficiency of the Evidence

Murder in the second degree is the "unlawful killing of a human being with malice aforethought." 18 U.S.C. § 1111(a). Boise argues that, because there was insufficient evidence of second degree murder, the district court erred when it denied his motion for judgment of acquittal under Fed.R. Crim.P. 29(c).

"[T]he critical inquiry on review of the sufficiency of the evidence to support a criminal conviction . . . [is] whether the record evidence could reasonably support a finding of guilty beyond a reasonable doubt." Jackson v. Virginia, 443 U.S. 307, 318, 99 S.Ct. 2781, 2788-89, 61 L.Ed.2d 560 (1979). Specifically, we ask whether "after viewing the evidence in the light most favorable to the prosecution, any rational trier of fact could have found the essential elements of the crime beyond a reasonable doubt." Id. at 319, 99 S.Ct. at 2789; United States v. Terry, 760 F.2d 939, 941 (9th Cir. 1985). We respect, however, the exclusive province of the jury to determine the credibility of witnesses, resolve evidentiary conflicts, and draw reasonable inferences from proven facts. United States v. Goode, 814 F.2d 1353, 1355 (9th Cir. 1987) (citing United States v. Ramos, 558 F.2d 545, 546 (9th Cir. 1977)).

Our review of the record in the light most favorable to the government convinces us that a rational jury could have found Boise guilty beyond a reasonable doubt of second degree murder. We acknowledge that the evidence here, as in most child-abuse cases, is circumstantial. But if such evidence is of sufficient quality to convince a jury beyond a reasonable doubt, we require no more. See Holland v. United States, 348 U.S. 121, 140, 75 S.Ct. 127, 137-38, 99 L.Ed. 150 (1954).

A. Evidence that Boise Killed Quinton

Quinton died from bilateral skull fractures that resulted in severe subdural hemorrhaging. In the three hours before Quinton died, Boise admitted he was the sole adult caring for the child. Doctors Lewman, Creelman and Nakamura testified that in their medical opinions the blows most likely "occurred shortly before death." Although they acknowledged that such blows could have occurred the day before Quinton's death or before Boise alone cared for him, in that situation the boy would have shown symptoms of a coma, unconsciousness, vomiting and an inability to eat. No such symptoms were observed.

Witnesses, including Quinton's mother, testified that he had acted normally the day before his death and earlier the day of his death. Boise's own medical expert, Dr. Brady, testified that this was not a "story of a continuous downhill progressive lethargy and change" and that there could well have been an injury very shortly before Quinton died. See United States v. Harris, 661 F.2d 138, 141 (10th Cir. 1981) (sufficient circumstantial evidence that defendant assaulted child where he admitted sole custody at the time when the child received the injuries which caused his death); United States v. Bowers, 660 F.2d 527, 529 (5th Cir. 1981) (evidence that child was battered coupled with proof that he was in sole custody of parent may well permit jury to infer that the parent injured him).

B. Evidence of Malice

Evaluating the facts and circumstances, the jury infers whether malice is present. See United States v. Fleming, 739 F.2d 945, 947 (4th Cir. 1984), cert. denied, 469 U.S. 1193, 105 S.Ct. 970, 83 L.Ed.2d 973 (1985).

Malice aforethought does not mean simply hatred or ill will, but also embraces the state of mind with which one intentionally commits a wrongful act without legal justification or excuse. It may be inferred from circumstances which show "a wanton and depraved spirit, a mind bent on evil mischief without regard to its consequences."

United States v. Celestine, 510 F.2d 457, 459 (9th Cir. 1975) (citing Government of Virgin Islands v. Lake, 362 F.2d 770 (3d Cir. 1966)).

From the circumstances of Quinton's death, the jury could rationally conclude beyond a reasonable doubt that Boise displayed "a wanton and depraved spirit, a mind bent on evil mischief without regard to its consequences." Celestine, 510 F.2d at 459. Physicians testified that Quinton died from two blunt force blows to the head that fractured his skull, causing subdural bleeding and swelling. They also testified that the injuries could not have been accidental, and were most likely caused when Quinton was hit with a hand or thrown against a wall.

There was also evidence that Quinton had been abused previously. Although a blunt force injury to the head was the immediate cause of death, Larry Lewman, the Oregon State Medical Examiner who performed the autopsy, discovered older head injuries that had caused brain hemorrhaging, a broken left arm and 15 broken ribs. He testified that the head-brain injuries were probably caused by violent shaking and that the broken ribs resulted from compression type squeezing.

The evidence showed that six-week old Quinton had received repeated beatings over a period of three and a half weeks and that, finally, two blows to the head, received when he was in Boise's care, killed him. From such evidence, the jury could rationally conclude beyond a reasonable doubt that Boise killed Quinton with malice aforethought.

II. Admissibility of Prior Injuries, Evidence of Battered-Child Syndrome and Photographs

We review the district court's evidentiary rulings for an abuse of discretion. United States v. Gillespie, 852 F.2d 475, 478-79 (9th Cir. 1988).

A. Autopsy Evidence of Prior Injuries

The district court admitted evidence of Quinton's prior injuries. Evidence of other crimes, wrongs, or acts is inadmissible under Fed.R.Evid. 404(b) to prove a person's character, but may be admissible for other purposes such as intent or absence of mistake or accident. The Supreme Court has addressed the question when similar act evidence is admissible under Rule 404(b). Huddleston v. United States, 485 U.S. 681, 108 S.Ct. 1496, 1499, 99 L.Ed.2d 771 (1988). There, the petitioner argued that the district court must "make a preliminary finding that the Government has proved the `other act' by a preponderance of the evidence before it submits the evidence to the jury." Id. 108 S.Ct. at 1497.

The Court found that the protection against unfair prejudice to the defendant came not from a requirement of a preliminary finding by the district court but from four other sources. Id. at 1502. A court should consider first whether under Rule 404(b) the evidence is probative of a material issue other than character. Id. at 1499, 1502.

It should next decide whether the evidence is relevant. Id. at 1502. In the Rule 404(b) context, the Court analyzed what it called "questions of relevance conditioned on a fact" under Fed.R.Evid. 104(b), and found that similar act evidence was relevant only if the jury could "reasonably conclude that the act occurred and that the defendant was the actor." Id. at 1501. In determining whether the government introduced sufficient evidence to meet Rule 104(b), the Court indicated that the district court should examine the evidence and decide whether the jury could reasonably find the condition by a preponderance of the evidence. Id.

After finding evidence of prior bad acts admissible, a court should determine whether under Fed.R.Evid. 403 the probative value of the similar acts evidence is substantially outweighed by its potential for unfair prejudice. Id. 108 S.Ct. at 1502. Finally, upon request, a court should instruct the jury under Fed.R.Evid. 105 that evidence of similar acts may be considered only for the proper purpose for which it is admitted. Id.

Boise contends that Quinton's prior injuries were inadmissible under Rule 404(b) because there was insufficient evidence to support a finding that he inflicted them. Applying Huddleston, we find that the district court did not abuse its discretion when it admitted the evidence. See United States v. Lewis, 837 F.2d 415, 418-19 (9th Cir.), cert. denied, 488 U.S. 923, 109 S.Ct. 304, 102 L.Ed.2d 323 (1988).

First, the prior abuse of Quinton was under Rule 404(b) probative of a material issue other than character; that is, it was evidence of malice and absence of accidental death. See Lewis, 837 F.2d at 419 (acts of prior abuse admissible to prove the defendant acted with malice aforethought); United States v. Leight, 818 F.2d 1297, 1301, 1303 (7th Cir.) (prior acts relevant to show malice, knowledge and absence of accident), cert. denied, 484 U.S. 958, 108 S.Ct. 356, 98 L.Ed.2d 381 (1987); United States v. Colvin, 614 F.2d 44, 45 (5th Cir.) (pattern of abuse admitted to prove malice aforethought), cert. denied, 446 U.S. 945, 100 S.Ct. 2174, 64 L.Ed.2d 802 (1980); United States v. Woods, 484 F.2d 127, 133-34 (4th Cir. 1973) (evidence admissible for any purpose other than to show a propensity or disposition to commit the crime), cert. denied, 415 U.S. 979, 94 S.Ct. 1566, 39 L.Ed.2d 875 (1974).

Second, the evidence of prior injuries was relevant under Huddleston only if the jury could reasonably conclude that the injuries occurred and that Boise inflicted them. The autopsy report revealed that Quinton had several prior injuries, including head injuries that had caused brain hemorrhaging, a broken left arm and 15 broken ribs. These were not accidental. The older head injuries, probably the result of excessive shaking, were inflicted a day or two before death. Boise was then the primary caretaker. Although Sheri Boise also had access to Quinton, she testified that she never shook him.

Quinton's left arm and 15 ribs were broken when the Boises were in Nevada. Although physicians could not pinpoint the exact date of injury, the evidence showed that Boise and his wife were the primary care-takers during March. There was no suggestion at trial that she mistreated the boy. She testified that she never squeezed him too hard and that she did not know how he was injured. There was evidence that Boise inflicted the fatal blows to the head. See Huddleston, 108 S.Ct. at 1502 (court reviews not only the direct evidence but also considers the evidence surrounding the crime actually charged). Given this evidence, the jury could reasonably have concluded that Boise inflicted the injuries. The court properly allowed this evidence to go to the jury. See Harris, 661 F.2d at 141 (sufficient circumstantial evidence to permit jury to infer that defendant struck child on prior occasions); Colvin, 614 F.2d at 45 (sufficient proof linking the appellant to prior injuries).

Third, Boise contends that the district court abused its discretion in admitting evidence of the prior injuries because under Fed.R.Evid. 403 the probative value was substantially outweighed by the danger of unfair prejudice. This argument lacks merit. Although that evidence may have been prejudicial, it was highly probative on the question of intent and absence of accident. See Lewis, 837 F.2d at 419 (prior abuse not excluded under Rule 403 because of probative value in disproving claims of intent or accidental death); Leight, 818 F.2d at 1304 (not abuse of discretion to conclude probative value of earlier child abuse outweighed unfair prejudice); Harris, 661 F.2d at 142; Colvin, 614 F.2d at 45.

The district court did not abuse its discretion when it admitted evidence of Quinton's prior injuries.

B. Admissibility of Battered-Child Syndrome

Although the immediate cause of death was two recent skull fractures, Lewman diagnosed Quinton as suffering from the battered-child syndrome. He described that as a generic, medical term applied to a group of injuries resulting from non-accidental causes but that the syndrome did not provide evidence of who injured the child. The prior head injuries caused by violent shaking, and the broken ribs caused by a compression type force, were indicative of the syndrome.

1. Relevance

Boise argues that evidence of the battered-child syndrome was inadmissible because it was irrelevant. We disagree. It was admissible as evidence of intent and of the absence of accident. See Bowers, 660 F.2d at 529 (proof that child suffers from battered-child syndrome may show that parent's explanation of injuries is a fabrication and that they occurred deliberately).

2. Qualification Under the Frye Test

Boise argues that the autopsy conclusion that Quinton died from the battered-child syndrome should not have been admitted without a finding that an established definition had gained general acceptance. When expert opinion based on a "`scientific principle or discovery' is proffered, `the thing from which the deduction is made must be sufficiently established to have gained general acceptance in the particular field in which it belongs.'" Gillespie, 852 F.2d at 480 (quoting Frye v. United States, 293 F. 1013, 1014 (D.C.Cir. 1923)). A proponent of scientific evidence that has yet to gain general judicial recognition must lay a proper foundation to show the underlying scientific basis and reliability of the testimony. Gillespie, 852 F.2d at 480.

Because battered-child syndrome has gained general judicial recognition, the proponent was not required to qualify it under Frye. Although circuit and state courts have not reviewed its admissibility under Frye, they have recognized it as an accepted medical diagnosis and have approved its use. See, e.g., McGuire v. Estelle, 902 F.2d 749, 754 (9th Cir. 1990); Bowers, 660 F.2d at 529; State v. Moyer, 151 Ariz. 253, 727 P.2d 31, 33 (Ct.App. 1986); People v. Jackson, 18 Cal.App.3d 504, 507, 95 Cal.Rptr. 919, 921 (1971); Smith v. State, 247 Ga. 612, 277 S.E.2d 678, 682 (1981); State v. Wilkerson, 295 N.C. 559, 247 S.E.2d 905, 911 (1978); State v. Goblirsch, 309 Minn. 401, 246 N.W.2d 12, 15 (1976); People v. Henson, 33 N.Y.2d 63, 349 N.Y.S.2d 657, 304 N.E.2d 358, 363-64 (1973); State v. Tanner, 675 P.2d 539, 543 (Utah 1983), superseded on other grounds, 743 P.2d 191 (Utah 1987); Meyers Carter, Proof of Physical Child Abuse, 53 Mo.L.Rev. 189, 203 (1988) ("Battered child syndrome is well accepted by medical science, and it should not be necessary to lay a foundation with regard to acceptance of the syndrome.").

C. Photographs

Boise argues that the use of an autopsy photograph was prejudicial under Rule 403. We find no abuse of discretion. See Bowers, 660 F.2d at 529-30 (admission of photograph of child's lacerated heart not an abuse of discretion); see also Batchelor v. Cupp, 693 F.2d 859, 865 (9th Cir. 1982) (admissibility of photographs of homicide victims was not unfairly prejudicial), cert. denied, 463 U.S. 1212, 103 S.Ct. 3547, 77 L.Ed.2d 1395 (1983).

III. Voir Dire

Examination or voir dire of prospective jurors protects a criminal defendant's Sixth Amendment right to an impartial jury. United States v. Giese, 597 F.2d 1170, 1181 (9th Cir.), cert. denied, 444 U.S. 979, 100 S.Ct. 480, 62 L.Ed.2d 405 (1979). The district court may conduct the examination, or it may allow counsel to examine prospective jurors. If it conducts the examination, it may allow the attorneys to supplement the questioning, or may itself ask additional questions as needed. Id.

The district judge has discretion in conducting voir dire and we will not find reversible error unless the questions asked or procedures used were so unreasonable as to constitute an abuse. United States v. Baldwin, 607 F.2d 1295, 1297 (9th Cir. 1979). We will not find an examination inadequate unless the judge failed to ask questions capable of revealing prejudices of prospective jurors. Giese, 597 F.2d at 1182.

Boise contends that the voir dire was inadequate because the judge did not conduct a "penetrating inquiry" of the prospective jurors' personal experiences with child abuse and possible racial bias. This contention is without merit.

The district judge conducted voir dire. She first questioned the prospective jurors about whether they had experiences with Native Americans and child abuse, and followed with questioning of individual jurors who responded affirmatively to the initial inquiries. She offered to talk privately in chambers with any juror who answered affirmatively to the sensitive question whether they personally had been victims of child abuse. Her questions would have revealed jurors' prejudices.

Boise also argues that voir dire was inadequate because the judge did not ask all of his questions. Rejecting a similar argument in Giese, we held that the district court "has considerable discretion to accept or reject proposed questions . . . and as long as it conducts an adequate voir dire, its rejection of a defendant's specific questions is not error." Giese, 597 F.2d at 1182-83. The judge did not abuse her discretion in rejecting some of counsel's questions.

Boise contends that voir dire was inadequate in light of pretrial publicity. "In a case of substantial pretrial publicity, the voir dire must not simply call for the jurors' subjective assessment of their own impartiality, and it must not be so general that it does not adequately probe the possibility of prejudice." United States v. Polizzi, 500 F.2d 856, 879 (1974), cert. denied, 419 U.S. 1120, 95 S.Ct. 802, 42 L.Ed.2d 820 (1975) (emphasis in original). A rigorous voir dire is necessary when pretrial publicity is great, but "[i]n cases of less publicity . . . [s]everal general questions addressed to the entire panel of jurors, followed by individual questioning of jurors who respond affirmatively to the initial inquiries, may be sufficient if it becomes clear that few jurors have any knowledge of the case." Giese, 597 F.2d at 1183.

The evidence shows clearly that these jurors had no knowledge of the case and that the publicity was not substantial enough to require lengthy examination. The newspaper articles submitted to the court dealt only with child abuse and none mentioned Boise or the death of his son. See United States v. McDonald, 576 F.2d 1350, 1354-55 (9th Cir.) (no substantial publicity where press coverage of land fraud schemes mentioned defendant only once), cert. denied, 439 U.S. 830, 99 S.Ct. 105, 58 L.Ed.2d 124; cert. denied, 439 U.S. 927, 99 S.Ct. 312, 58 L.Ed.2d 320 (1978). Having established that the jurors had no knowledge of the case, there was no need for the judge to follow with additional inquiries. "Further questioning may have only fanned the embers of incipient prejudice by arousing curiosity." United States v. Flores-Elias, 650 F.2d 1149, 1150-51 (9th Cir.) (widespread press coverage of smuggling illegal aliens mentioned defendant only once), cert. denied, 454 U.S. 904, 102 S.Ct. 412, 70 L.Ed.2d 223 (1981) (citing Beck v. Washington, 369 U.S. 541, 82 S.Ct. 955, 8 L.Ed.2d 98 (1962)).

The district judge did not abuse her discretion and her voir dire was adequate in all respects.

IV. Sentencing Guidelines

A. Retroactive Application of Mistretta

The district court applied the Sentencing Guidelines. Although the defendant committed this crime when the Sentencing Guidelines were in effect, at the time of trial this court had declared them unconstitutional. See Gubiensio-Ortiz v. Kanahele, 857 F.2d 1245 (9th Cir. 1988), vacated sub nom. United States v. Chavez-Sanchez, 488 U.S. 1036, 109 S.Ct. 859, 102 L.Ed.2d 984 (1989). By the time of sentencing the Supreme Court had held the Guidelines constitutional, implicitly overruling Gubiensio-Ortiz. See Mistretta v. United States, 488 U.S. 361, 109 S.Ct. 647, 102 L.Ed.2d 714 (1989).

Boise argues that he detrimentally relied on the unconstitutionality of the Guidelines in deciding to go to trial and in making strategic trial decisions. He contends that the retroactive application of Mistretta denied him fundamental fairness and due process.

We rejected a similar retroactivity argument in United States v. Kincaid, 898 F.2d 110, 111 (9th Cir. 1990). There, the Guidelines were in effect when Kincaid committed a crime but were unconstitutional when he pleaded guilty. The district court sentenced him under the Guidelines after Mistretta. On appeal he argued that Mistretta should not be applied retroactively to pleas made while the Guidelines were unconstitutional. We held that his detrimental reliance on Gubiensio-Ortiz did not constitute a "substantially inequitable result" which would preclude retroactivity. Id.

The Guidelines were in effect at the time of this crime. The only difference with Kincaid is that Boise went to trial. We see no reason to treat the two cases differently. Boise and his attorney were "on notice that the Guidelines were in effect and that the Supreme Court might vacate [ Gubiensio-Ortiz]." United States v. Gonzalez-Sandoval, 894 F.2d 1043, 1053 (9th Cir. 1990). The retroactivity analysis in Kincaid applies equally to a decision to go to trial and one to plead guilty.

B. Applicability of the Vulnerable Victim Adjustment

The district court determined that the vulnerable victim adjustment applied to Boise and increased his offense level by two. He argues that the Commentary to the vulnerable victim guideline requires a defendant to select a victim intentionally because of his vulnerability. We disagree. Under Sentencing Guidelines Ch. 3, Part A, § 3A1.1, a court is to increase an offense level by two "[i]f the defendant knew or should have known that a victim of the offense was unusually vulnerable due to age, physical or mental condition, or that a victim was otherwise particularly susceptible to the criminal conduct." The Commentary states that an adjustment is to be made when:

an unusually vulnerable victim is made a target of criminal activity by the defendant. The adjustment would apply, for example, in a fraud case where the defendant marketed an ineffective cancer cure or in a robbery where the defendant selected a handicapped victim. But it would not apply . . . where the defendant sold fraudulent securities by mail to the general public and one of the victims happened to be senile.

Boise's son was a vulnerable victim for purposes of adjusting the base offense level because a six-week old infant is "unusually vulnerable due to age," not because Boise selected him because of his vulnerability. Cf. United States v. Roberson, 872 F.2d 597, 608-09 (5th Cir.) (84-year old man is a vulnerable victim due to age), cert. denied, ___ U.S. ___, 110 S.Ct. 175, 107 L.Ed.2d 131 (1989).

We find that the district judge's application of the vulnerable victim adjustment was proper.

C. Constitutionality of the Guidelines

Boise contends that the Guidelines violate the separation of powers doctrine. He argues that, when the probation officer recommended that the court apply the vulnerable victim guideline, he was an advocate as a member of the judicial branch. We rejected this argument in United States v. Belgard, 894 F.2d 1092, 1096-99 (9th Cir. 1990). We held that the probation officer's involvement in sentencing did not violate either the separation of powers doctrine or due process because the officer's report is not binding on the judge and the court's power to appoint an independent investigator to gather information for sentencing is consistent with prior Supreme Court holdings. Id.

V. Conclusion

We find sufficient evidence to support the jury's determination that Boise killed Quinton with malice aforethought. The district court did not abuse its discretion when it admitted evidence of the battered-child syndrome and of prior injuries and when it admitted the photographs. Its voir dire was adequate and it properly applied the Sentencing Guidelines.

AFFIRMED.