State of Arizona, Appellee v. Stephen Jay Malone Jr., Appellant.

Summary

The court held that expert evidence of brain damage is inadmissible when offered to corroborate a defendant’s character trait for impulsivity and thereby undermine premeditation. Although Arizona permits behavioral-tendency evidence showing impulsivity, mental-disease-or-defect evidence may not be used to negate mens rea, whether by showing incapacity or merely a reduced likelihood of premeditation. The court vacated the court of appeals’ opinion and affirmed Malone’s convictions and sentences.