Finally, we review for abuse of discretion a trial court's determination that an evidentiary item's chain of custody has been sufficiently established. See United States v. Ricco, 52 F.3d 58, 61 (4th Cir.1995). III.

This rule is not intended to be "iron-clad" and is satisfied by "sufficient proof that the evidence is what it purports to be and has not been altered in any material respect[.]" United States v. Ricco, 52 F.3d 58, 61-62 (4th Cir. 1995). The rule is not intended to require exclusion of real evidence based on a missing link in its custody.

This showing is satisfied by "sufficient proof that the evidence is what it purports to be and has not been altered in any material respect," and is not intended as an "iron-clad" rule that requires exclusion of real evidence based on a missing link in its custody. United States v. Ricco, 52 F.3d 58, 61-62 (4th Cir. 1995). Resolution of a chain of custody question rests with the sound discretion of the trial judge.

Consistent with this rule, we have held that the failure to make a pretrial motion to suppress precludes the defendant from raising on appeal a constitutional challenge to the admission of that evidence. See United States v. Ricco, 52 F.3d 58, 62 (4th Cir. 1995) (holding that defendant "waived the right to assert his constitutional objections" to the admission of evidence "by failing to file a motion to suppress the evidence before trial"). This waiver principle applies here, where Wright contends, for the first time on appeal, that the jailhouse informant's testimony should have been suppressed under the Sixth Amendment.

Harris, however, has waived this argument by failing to raise it as a distinct ground in support of his motion to suppress in the district court. See Fed. R. Crim. P. 12(b)(3), (e); United States v. Ricco, 52 F.3d 58, 62 (4th Cir. 1995) (concluding that "[a]ny failure to file a pre-trial motion to suppress constitutes waiver of the defense or objection unless the defendant can demonstrate just cause for the failure."); see also United States v. Horton, 756 F.3d 569, 574 (8th Cir. 2014) (holding arguments not raised in motion to suppress are waived on appeal), petition for cert. filed, ___ U.S.L.W. ___ (U.S. June 3, 2014) (No. 13-10476); United States v. Lockett, 406 F.3d 207, 212 (3d Cir. 2005) ("[I]n the context of a motion to suppress, a defendant must have advanced substantially the same theories of suppression in the district court as he or she seeks to rely upon in this [c]ourt.").

Learning new information by the end of trial does not alone support a good cause finding for delay. See United States v. Wilson, 115 F.3d 1185, 1190–91 (4th Cir.1997) ; United States v. Ricco, 52 F.3d 58, 62 (4th Cir.1995). For one thing, Moore and his attorney were aware of the alleged stop at the start of trial. In fact, he had previously attempted, unsuccessfully, to suppress evidence from the apartment search on Fourth Amendment grounds.

Accordingly, we conclude that his new claims are waived. See Fed. R. Crim. P. 12(b)(3), (e); United States v. Ricco, 52 F.3d 58, 62 (4th Cir. 1995); see also United States v. Green, 691 F.3d 960, 963-64 (8th Cir. 2012) ("[T]he waiver provision of Rule 12 precludes appellate review of arguments to suppress evidence that are not raised in a pretrial motion to suppress."); United States v. Lockett, 406 F.3d 207, 212 (3d Cir. 2005) ("[I]n the context of a motion to suppress, a defendant must have advanced substantially the same theories of suppression in the district court as he . . . seeks to rely upon in this [c]ourt."). Even if Craig had not waived these new claims, we conclude that the district court did not plainly err in denying his motion to suppress.

Smith provides no rationale explaining why the powder cocaine properly attributed to him as relevant conduct by the district court should not have been converted into crack, and we conclude that Smith has failed to demonstrate that the district court clearly erred in this regard. See id.; United States v. Ricco, 52 F.3d 58, 63 (4th Cir. 1995) (approving 100:88 powder-to-crack conversion ratio). Assuming, as Smith asserts, that certain transactions should not have been attributed to him, they have no impact on his Guidelines range. Because the drug weight is amply supported by the testimony of Smith's co- defendants, the district court did not clearly err in finding Smith responsible for 1598.6 grams of crack cocaine.

"Establishing a strict chain of custody 'is not an iron-clad requirement, and the fact of a missing link does not prevent the admission of real evidence, so long as there is sufficient proof that the evidence is what it purports to be and has not been altered in any material respect.'" Id. at *7, quoting United States v. Ricco, 52 F.3d 58, 61-62 (4th Cir. 1995). Upon review of the record, we are satisfied that the district court did not abuse its discretion in admitting the challenged evidence.

Failure to make a motion to suppress before trial constitutes a waiver unless the trial court grants relief from the waiver under Rule 12(e) for cause shown. Fed.R.Crim.P. 12(e); United States v. Ricco, 52 F.3d 58, 62 (4th Cir. 1995). The district court has not granted such relief.