In this murder case, the Supreme Court determined that the defendant’s Sixth Amendment right to confront witnesses against him was violated when the trial court admitted into evidence a transcript of another person’s plea allocution.  In 2006, a child in the Bronx was killed by a stray 9-millimeter bullet.  Following an investigation that included officers discovering a 9-millimeter cartridge in his bedroom, Nicholas Morris was charged with the murder but resolved the case by accepting a deal where he pleaded guilty to criminal possession of a .357-magnum revolver in exchange for dismissal of the murder charge.  Years later, the defendant Hemphill was charged with the murder.  At trial, for which Morris was unavailable as a witness, Hemphill pursued a third-party culpability defense and elicited undisputed testimony from the State’s law enforcement officer witness indicating that a 9-millimeter cartridge was discovered in Morris’s bedroom.  Over Hemphill’s Confrontation Clause objection, the trial court permitted the State to introduce Morris’s plea allocution for purposes of proving, as the State put it in closing argument, that possession of a .357 revolver, not murder, was “the crime [Morris] actually committed.”  Relying on state case law, the trial court reasoned that Hemphill had opened the door to admission of the plea allocution by raising the issue of Morris’s apparent possession of the 9-millimeter cartridge.

After finding that Hemphill had preserved his argument by presenting it in state court and accepting without deciding that the plea allocution was testimonial, the Supreme Court determined that admission of Morris’s plea allocution violated Hemphill’s confrontation rights and rejected various arguments from the State advocating for an “opening the door” rule along the lines of that adopted by the trial court.  Describing the “door-opening principle” as a “substantive principle of evidence that dictates what material is relevant and admissible in a case” the Court distinguished it from procedural rules, such as those described in Melendez-Diaz, that the Court has said properly may govern the exercise of the right to confrontation.  The Court explained that it “has not held that defendants can ‘open the door’ to violations of constitutional requirements merely by making evidence relevant to contradict their defense.”  Thus, the Court reversed the judgment of the New York Court of Appeals which had affirmed the trial court.

Justice Alito, joined by Justice Kavanaugh, concurred but wrote separately to address the conditions under which a defendant can be deemed to have validly waived the right to confront adverse witnesses.  Justice Alito wrote that while it did not occur in this case, there are circumstances “under which a defendant’s introduction of evidence may be regarded as an implicit waiver of the right to object to the prosecution’s use of evidence that might otherwise be barred by the Confrontation Clause.”  He identified such a situation as that where a defendant introduces a statement from an unavailable witness, saying that the rule of completeness dictates that a defendant should not be permitted to then lodge a confrontation objection to the introduction of additional related statements by the witness.

Justice Thomas dissented based on his view that the Court lacked jurisdiction to review the decision of the New York Court of Appeals because Hemphill did not adequately raise his Sixth Amendment claim there.