Cite as: 523 U. S. 303 (1998)
Stevens, J., dissenting
III
The constitutional requirement that a blanket exclusion of potentially unreliable evidence must be proportionate to the purposes served by the rule obviously makes it necessary to evaluate the interests on both sides of the balance. Today the Court all but ignores the strength of the defendant's interest in having polygraph evidence admitted in certain cases. As the facts of this case illustrate, the Court is quite wrong in assuming that the impact of Rule 707 on respond-ent's defense was not significant because it did not preclude the introduction of any "factual evidence" or prevent him from conveying "his version of the facts to the court-martial members." Ante, at 317. Under such reasoning, a rule that excluded the testimony of alibi witnesses would not be significant as long as the defendant is free to testify himself. But given the defendant's strong interest in the outcome— an interest that was sufficient to make his testimony presumptively untrustworthy and therefore inadmissible at common law—his uncorroborated testimony is certain to be less persuasive than that of a third-party witness. A rule that bars him "from introducing expert opinion testimony to bolster his own credibility," ibid., unquestionably impairs any "meaningful opportunity to present a complete defense"; indeed, it is sure to be outcome determinative in many cases.
Moreover, in this case the results of the polygraph test, taken just three days after the urinalysis, constitute independent factual evidence that is not otherwise available and that strongly supports his defense of "innocent ingestion." Just as flight or other evidence of "consciousness of guilt" may sometimes be relevant, on some occasions evidence of "consciousness of innocence" may also be relevant to the central issue at trial. Both the answers to the questions propounded by the examiner, and the physical manifestations produced by those utterances, were probative of an innocent state of mind shortly after he ingested the drugs. In Dean Wigmore's view, both "conduct" and "utterances" may con-
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