From the Kentucky Supreme Court, in Sevier v. Commonwealth (Ky. June 19, 2014):

At the start of this joint trial, the trial court seated thirteen jurors to hear the evidence, a practice authorized by Kentucky Rules of Criminal Procedure (RCr) 9.32(1). Seating more [than] the minimum number of twelve jurors to hear the evidence is a routine precautionary measure taken by trial courts against the situation that might occur should one or more jurors be unable to complete the trial, reducing the number of jurors below the requisite twelve-member jury to decide the case.

When a trial court chooses to seat more than twelve jurors, all of them are sworn as members of the petit jury; and all of them participate as such until immediately before the trial court submits the case to the jury for deliberations. At that point, Civil Rule (CR) 47.03 requires the court clerk to reduce the jury to twelve by selecting at random those to be declared the alternates and dismissed from the jury. But, in this case, the trial court erroneously failed to select an alternate at the time contemplated by CR 47.03. The jury retired to the jury room, completed deliberation, and announced that it had reached a verdict in the guilt phase of the trial before the trial court and the parties discovered that an alternate juror had not been selected and excused from the jury….

Sevier urges this Court to look to other states that presume prejudice when more than twelve jurors participate in deliberation. This appears to be the majority position among the jurisdictions that have tackled this issue because most of them have opted to apply either a rebuttable or an irrebuttable presumption of prejudice to the defendant. [The court concludes, though, that those out-of-jurisdiction cases turned on state law approaches that are different from Kentucky’s:-EV] In [those cases], the alternate jurors were identified and labeled a stranger to the jury room and the verdict. That is different from the manner in which the alternate was selected in Sevier’s case because Kentucky law considers all thirteen jurors to be fully participating members of the petit jury until one is randomly selected to be dismissed as the alternate….

The presence of a “stranger” during deliberations is often viewed as a threat to the jury’s secrecy and ability to engage in free discussion as a cohesive group without worry of later dissemination. But, in Kentucky, when the complement of thirteen jurors is permitted to deliberate without an alternate being named or removed before reaching a verdict, there is there is no stranger in the jury room. Instead, the jury constitutes all thirteen members who, as in Sevier’s case, endeavor to reach a unanimous verdict for which all members are accountable.

That is, there can be no stranger to the proceedings because absent the court labeling a juror as such, each juror was a potential alternate. Further, the concerns that other courts have expressed regarding the potential chilling effect or risk of dissemination of confidential information regarding deliberations are unfounded when all thirteen members are considered to be, and treated as, jurors. When none of the thirteen jurors is operating under the status of alternate, the discussion and verdict information that courts who presume prejudice are concerned with protecting belong just as much to the thirteenth juror as they do the other twelve because the thirteenth juror played just as much of a role in reaching the verdict and as the other twelve jurors….

[W]e first address Sevier’s allegation that he was constitutionally entitled to a jury of exactly twelve jurors.

Section Seven of the Kentucky Constitution states that “[t]he ancient mode of trial by jury shall … remain inviolate, subject to such modifications as may be authorized by this Constitution.” … [T]he inclusion of the phrase, “the ancient mode,” was clearly intended to maintain the constitutional import of the traditional practice of using a twelve-person jury. The record of the Constitutional Convention made this intent clear, with representatives believing that removing the phrase “ancient mode” from the constitution would send a signal to the judiciary that “the change in language was intended to reflect a change in the law, a departure from the common-law jury in favor of a legislative jury[.]” …

Although it is clear that absent a personal waiver, it is a violation of Section Seven of the Kentucky Constitution for a defendant to be tried by a jury of less than twelve members, this principle of Kentucky Constitutional law has only been applied where defendants were tried by juries comprised of less than twelve jurors. We have found no cases decided since the adoption of the present constitution that assess the constitutionality of a jury verdict procured by the unanimous decision of thirteen qualified jurors. We now have occasion to determine if this “occult virtue in the number twelve [ ]” equally applies when a defendant is provided with more than twelve jurors.

This country’s reliance on twelve jurors as the cornerstone of the trial by jury has been labeled “a historic[ ] accident” because of the minimal insight we have into its origins. As the Supreme Court noted in Williams v. Florida, many of these justifications “rest on little more than mystical or superstitious insights into the significance of ’12.’ “68 One such example is the connection drawn by Lord Coke between the number twelve and the holy writ, with particular reference to “12 apostles, 12 stones, [and] 12 tribes[.]” Regardless of the reason behind twelve-member juries being given a constitutional prominence, case law is full of references to larger juries as favoring criminal defendants….

Based on the foregoing, today we choose to deviate from the strict application of the twelve-member jury rule as a constitutional question in instances where that number is increased. Section Seven of the Kentucky Constitution and our case law construing that provision make clear that a defendant is entitled to a jury of twelve. It is equally clear that both state and federal constitutional protections serve as a “floor” in setting the minimum level of protections that must be afforded to citizens.

As a result, states are free to provide citizens with additional protections above-and-beyond the constitutional “floor” without contravening the constitution or its intent. We hold that the trial court erred in allowing a thirteen-person jury to deliberate in determining Sevier’s guilt, but the error was not an error of constitutional import because it provided Sevier with protections in excess of those mandated by Section Seven of the Kentucky Constitution….

Absent an error of constitutional magnitude, we cannot find that the trial court error was anything other than harmless and certainly not jurisprudentially intolerable to the level of palpable error because the verdict was unanimous. Sevier makes no concrete factual allegations from which prejudice may be derived in the absence of a presumption or inference of prejudice. In fact, it was the Commonwealth that was most clearly at risk by the inclusion of the thirteenth juror. Even though the jury contained an additional juror, the Commonwealth nonetheless bore the burden of proving Sevier’s guilt beyond a reasonable doubt and obtaining a unanimous verdict of guilty in order to achieve a conviction. So we do not find the trial court’s failure to reduce the jury to twelve to be reversible error.

But what if one of them betrayed him?