United States Supreme Court (May 1, 2006)
A defendant has a constitutional right to present probative, nonprejudicial evidence that another may have committed the crime.
At Holmes' trial for murder and related crimes, the prosecution's case was strongly supported by forensic evidence that overwhelmingly established his guilt. In his defense, in addition to attacking the forensic evidence, Holmes sought to establish that another man, White, committed the crimes. Holmes' evidence showed that White admitted (out-of-court) that he killed the victim, he was in the area of the murder at the time it was committed, and White's proffered alibi had been refuted by another witness. The evidence was excluded under a South Carolina rule which states that where "there is strong evidence of guilt, especially where there is strong forensic evidence, the proffered evidence about a third party's alleged guilt does not raise a reasonable inference as to the defendant's own innocence." Holmes was found guilty and sentenced to death.
On direct review, Justice Alito, writing for a unanimous Court, reversed Holmes' conviction and held that South Carolina's mechanism to exclude third party culprit evidence violated his right to a meaningful opportunity to present a complete defense. The problem with the rule was that it did not focus on the probative value or the potential adverse effects of admitting the defense evidence of third-party guilt. Instead, the critical inquiry concerned the strength of the prosecution's case, which made the rule arbitrary.
In Massachusetts, a defendant is entitled to present evidence that another person committed the crime. To be admissible, the evidence must be relevant, not too remote or speculative, and must not confuse the jury by diverting their attention to collateral matters. If such evidence is of substantial probative value, and will not tend to prejudice or confuse, all doubt should be resolved in favor of admissibility. Commonwealth v. Phinney, 446 Mass. 155, 163 (2006)