Today the Houston Institute filed an amicus brief in the case of Leonard v. Simpson at the United States Supreme Court. We argue that post-conviction mitigation evidence substantially differing in degree from mitigation evidence adduced during the penalty phase of trial can suffice to establish prejudice under Strickland‘s test for ineffective assistance of counsel. The circuits are split on whether mitigation evidence must differ in degree and kind versus degree or kind, and the “degree and kind” barrier violates Strickland by precluding a determination of whether there exists a reasonable probability that the sentencer would have concluded the balance of aggravating and mitigating circumstances did not warrant death. Indeed, the degree and kind barrier conflicts with over two decades’ worth of Supreme Court Strickland jurisprudence.
Social science research proves that evidence differing in degree but not kind can alter the persuasive effect of a defendant’s mitigation case. Corroboration permits the jury to obtain an independent evaluation of a defendant’s social history, thereby making mitigation testimony credible, memorable, and persuasive. Interviews with former capital jurors confirm the empirical evidence suggesting that corroboration enhances persuasive effect. Mitigation evidence that portrays a defendant’s social history comprehensively and accurately enhances the jury’s objective decision-making. Family member testimony humanizes a defendant by creating an opportunity for jurors to sympathize with the defendant and his family. All in all, evidence differing in degree should be sufficient under Strickland‘s test.
Read our brief: