Juror Disqualification and Substitution. The Federal Rules of Criminal Procedure provide for the substitution of alternate jurors to replace “jurors who are unable to perform or who are disqualified from performing their duties.” Failure to object in a timely manner to the substitution of a juror or dismissal of an alternate juror constitutes a waiver of the objection. The judge may allow the parties to stipulate to a jury of fewer than twelve persons if jurors are excused for good cause. Once the jury retires to consider its verdict, the trial court has sole discretion to excuse a juror for good cause and to allow the remaining eleven jurors to return a valid verdict.