A California jury convicted respondent Pinholster on two counts of first-degree murder. At the penalty phase before the same jury, the prosecution produced eight witnesses, who testified about Pinholster’s history of threatening and violent behavior. Pinholster’s trial counsel, who unsuccessfully sought to exclude the aggravating evidence on the ground that the prosecution had not given Pinholster proper notice under California law, called only Pinholster’s mother. Counsel did not call a psychiatrist, though they had consulted with Dr. Stalberg, who had diagnosed Pinholster with antisocial personality disorder. The jury recommended the death penalty, and Pinholster was sentenced to death. Pinholster twice sought habeas relief in the California Supreme Court, alleging, inter alia , that his trial counsel had failed to adequately investigate and present mitigating evidence during the penalty phase. He introduced additional evidence to support his claim: school, medical, and legal records; and declarations from family members, one of his trial attorneys, and Dr. Woods, a psychiatrist who diagnosed him with bipolar mood disorder and seizure disorders, and who criticized Dr. Stalberg’s report. Each time, the State Supreme Court unanimously and summarily denied the claim on the merits. Subsequently, a Federal District Court held an evidentiary hearing and granted Pinholster federal habeas relief under 28 U. S. C. §2254. Affirming, the en banc Ninth Circuit considered the new evidence adduced in the District Court hearing and held that the State Supreme Court’s decision “involved an unreasonable application of… clearly established Federal law,” §2254(d)(1).
Held:
