Strict application of ex post facto principles... would unduly impair the incremental and reasoned development of precedent that is the foundation of the common law system."

The decision did not affect the requirement of fair warning placed on statutes passed by legislatures - "The Constitution's Ex Post Facto Clause... 'is a limitation upon the powers of the Legislature, and does not of its own force apply to the Judicial Branch of government'... a judicial alteration of a common law doctrine of criminal law [only] violates the principal of fair warning... where it is 'unexpected and indefensible by reference to the law which had been expressed prior to the conduct in issue.The case was about a murderer, Wilbert Rogers, who stabbed his victim in the heart, causing the victim to have cardiac arrest and lapse into a coma.

Rogers was convicted of second-degree murder under Tennessee's homicide statute, which does not include the year and a day rule.

Rogers had also argued that abolishing the rule after he had committed his crime would violate the Ex Post Facto Clause of Article I of the U.S. Constitution.

The Court evaluated this case under the rubric of due process rather than the limitations on ex post facto lawmaking present in the Constitution.

Thirteenth century medical science was not capable of determining the cause of death beyond a reasonable doubt after a significant amount of time had elapsed following the ultimately fatal blow.

However, as medical science has advanced, forensic scientists have been able to determine the cause of a person's death later and later after the fatal event occurs.

"For this reason, the year and a day rule has been legislatively or judicially abolished in the vast majority of jurisdictions recently to have addressed the issue," as the Tennessee Supreme Court observed.

Accordingly, it was hardly unexpected and indefensible for the Tennessee Supreme Court, while considering an appeal from Rogers's own conviction, to first formally abolish the rule and then to apply that decision retroactively to his own case.

Applying his originalist understanding of the Ex Post Facto Clause, Justice Scalia concluded that the Tennessee Supreme Court's retroactive application of its decision to remove the year-and-a-day rule from its jurisprudence rendered Rogers's conviction for murder invalid.

Scalia began with a different premise than the majority—that the Tennessee Supreme Court had changed that state's law of murder when it abolished the year-and-a-day rule in Rogers's case.

Under accepted norms of judicial process [that prevailed in the time of the Framers], an ex post facto law... was simply not an option for the courts.For these historical reasons, Scalia believed, the majority should not have circumvented the strictures of the Ex Post Facto Clause by analyzing what the Tennessee Supreme Court had done under the rubric of due process.