A constitutionally deficient investigation calls into question the reasonableness of counsel’s defense theory. The prejudice analysis for a claim of ineffective assistance of counsel is not whether he has presented a reasonable theory in the abstract. Prejudice under the standard of Strickland v. Washington (1984) 466 U.S. 668 must take into account the significant mental and psychological impairments which counsel could have discovered and presented along with the mitigation evidence that was presented to assess whether there is a reasonable probability that there would have been a different sentence. The state court found that trial counsel was constitutionally deficient. Counsel’s representation fell below the objective standard of reasonableness. There was cursory investigation about mitigation for the penalty phase of a death penalty case. Trial counsel spent one day talking with witnesses who were selected by Sears’ mother. The defense presented seven witnesses who offered testimony that Sears was from a middle-class background; his relatives were shocked and dismayed by what he had done; and, the imposition of a death sentence would devastate the family. Despite the lack of investigation as a basis for an informed tactical decision, the state court found that Sears did not meet the prejudice prong of the ineffective assistance of counsel claim. Because counsel had a theory and presented some mitigation evidence, the state court reasoned that Sears failed to meet his burden of proving that there is a reasonable likelihood that the outcome at trial would have been different if a different mitigation theory had been presented. Post-conviction investigation revealed that Sears was the product of a physically abusive relationship; he was sexually abused by an adolescent cousin; his parents were both verbally abusive and his father disciplined him with age-inappropriate military drills. Sears demonstrated behavior problems from a young age and was found to be severely learning disabled and severely behaviorally handicapped by high school. Two psychological experts with unchallenged credentials found he had substantial deficits in mental cognition and reasoning and significant frontal lobe abnormalities. Whatever the source of the brain damage, he placed below the first percentile in several categories of cognitive functioning. Some adverse evidence could have been explained as a feature of his profound personality disorder. The evidence would not have made Sears more likeable to the jury, but it would have helped the jury to understand Sears and place his horrendous crimes in context. The case was reversed and remanded for the state to undertake the appropriate prejudice analysis.