Was counsel's failure to investigate and present a diminished capacity defense prejudicial under Strickland v. Washington?

QUESTIONS PRESENTED 1. Counsel admitted that he did not know that his chosen defense, diminished capacity, could be based upon mental illness. As a result, counsel never investigated Mr. Hernandez’s history of mental illness, head injuries, and child abuse—which multiple habeas experts said could negate intent to commit first degree murder. Was such failure prejudicial in light of the available diminished capacity defense at the time of trial and did the Ninth Circuit Court of Appeals err in failing to appropriately apply California law in conducting the prejudice analysis under Strickland v. Washington, 466 U.S. 668 (1984)? 2. Did the Ninth Circuit incorrectly invade the province of the jury when it characterized the unrebutted expert opinions as “weak” when conducting the Strickland v. Washington prejudice analysis? 3. Did the Ninth Circuit fail to provide meaningful appellate review when it arbitrarily reversed a grant of guilt phase habeas relief in a capital case after two members of the original panel died? 1On August 16, 2011, the district court granted penalty phase habeas relief on multiple grounds, including ineffective assistance of counsel for failure to investigate and present mitigation evidence.