In United States v. Cencer, 90 F.3d 1103 (6th Cir. 1996), the court held that the prohibition in Rule 24(c) against substituting alternate jurors after submission of the case to the original jury can be waived.
There, immediately before closing arguments on a Friday morning, the trial judge reminded counsel that two of the 12 regular jurors could not stay to deliberate during the following week, and suggested that two alternate jurors sit in on the deliberations so they could be substituted for regular jurors, if necessary.
Counsel for both parties affirmatively agreed to that procedure.
Ultimately, during deliberations, the trial court substituted the two alternate jurors for the two regular jurors who had to leave.
The defendant did not object to the substitutions (nor did the government). After convictions were returned, the defendant appealed, arguing that the trial court had erred by not following the requirements of Rule 24(c); that he did not waive the requirements of Rule 24(c); and that, while he had forfeited his right to challenge the court's error, by not objecting, that error was subject to plain error review.
The appellate court held that the defendant had waived the requirements of Rule 24(c), not forfeited his right to object to them, and hence there was no error on the part of the court in not adhering to the requirements of that rule.
In so holding, the court made the following comment:
In sum, we hold that where, as here, the defendant affirmatively consents to a procedure in which alternate jurors are silently present during initial jury deliberations, in anticipation of a possible substitution, and alternates ultimately are substituted, the defendant waives any challenge to such a procedure under Rule 24(c). Naturally, though, the defendant does not necessarily waive all related objections. For example, as in the instant case, the defendant can still object to any jury instructions concerning the substitution, and if satisfactory procedures for substitution cannot be devised, he may certainly be permitted to withdraw his consent before it is too late. Here, however, the defendant did not attempt to retract his consent to substitution. Id. at 1109.