In 1981, in the course of a burglary, Fernando Belmontes bludgeoned a woman to death. He was convicted of murder and sentenced to death, and his conviction and sentence were affirmed on direct appeal in California state courts. When he then sought habeas corpus relief from the federal courts, the district court denied the writ, but the Court of Appeals for the Ninth Circuit reversed. It first held that the jury instructions had been erroneous, but then, after the Supreme Court reversed that decision in 2006, held that Belmontes had been denied effective assistance of counsel, in that his lawyer failed to present all available mitigating evidence in the sentencing phase.
The Supreme Court granted the petition for a writ of certiorari and, without setting the case for argument, reversed the Ninth Circuit Court's decision in a per curiam opinion. The Court observed that, to prevail on a claim of ineffective assistance, a defendant must establish both that the trial lawyer's performance failed to meet an objective standard of reasonableness and that the failure was prejudicial, i.e., that there was a reasonable probability that the jury would have imposed a different sentence if the alleged failure had not occurred. Strickland v. Washington, 466 U.S. 668 (1984). The prejudice prong of this test requires consideration of the likely effect on the jury not only of mitigating evidence that was not offered, but also of any aggravating evidence that would have become admissible if the unoffered evidence had been received. In this case, while the Court implied that it had strong doubts about whether the performance of Belmontes's lawyer was objectively deficient, it declined to decide that question, because any failure that may have occurred was not prejudicial. The lawyer needed to tailor the evidence that he presented in the sentencing phase of the trial very carefully to avoid opening the door to evidence (which he had succeeded in excluding from the prosecution's case-in-chief on sentencing) that Belmontes had previously committed another, even-more-brutal murder but had had been convicted only of a lesser offense. In view of this aggravating evidence, the Court termed "fanciful" the notion that the sentencing result would have been different if the lawyer had offered the additional evidence to which the court of appeals pointed as having been unprofessionally overlooked.
Justice Stevens filed a concurring opinion.