United States v. Scheffer

Justice Thomas's opinion stated that "legitimate interests" were served by excluding polygraph evidence--namely that "there is simply no consensus that polygraph evidence is reliable." He offered two other "legitimate interests" ("the jury's core function of making credibility determinations in criminal trials" and "avoiding litigation over issues other than the guilt or innocence of the accused"). Thomas was joined by a plurality.

These "legitimate interests" were essentially those cited by the military judge in the court-martial, whose ruling the Court upheld inasmuch as it reversed the decision of the appeals court. In presenting his response to the three "legitimate interest" questions, Justice Thomas noted that "A defendant's right to present relevant evidence is subject to reasonable restrictions to accommodate other legitimate interests in the criminal trial process." For this reason, there are rules governing the introduction or exclusion of evidence, and as long as they cannot be deemed "arbitrary" or "disproportionate to the purposes they are designed to serve," they do not infringe on the defendant's Sixth Amendment rights. Only when a rule excluding evidence denies "a weighty interest of the accused," Justice Thomas wrote, can it be considered arbitrary or disproportionate. In the present instance, Rule 707 "serves the legitimate interest of ensuring that only reliable evidence is introduced." Justice Thomas then cited the great body of literature which questions the validity of polygraph results, as well as the view that, unlike other expert witnesses, a polygraph examiner in effect supplants the jury by offering simply one more opinion. Addressing the third "legitimate interest," he mentioned some of the ancillary (and time-consuming) disputes that would inevitably arise if polygraph evidence were allowed into the courtroom.