State v. Mott
In State v. Mott, 187 Ariz. 536, 931 P.2d 1046 (1997), the Arizona Supreme Court rejected the diminished capacity defense and held testimony of a mental health professional about a defendant's mental incapacity owing to a mental disease or defect is only admissible in the context of an insanity defense. 187 Ariz. at 540-41, 931 P.2d at 1050-51.
In the absence of an insanity defense, the court concluded such evidence is inadmissible to challenge the element of mens rea, that is, what mental state the state must prove the defendant had for the crime to be committed. Id. at 541, 931 P.2d at 1051.
But the court noted that its holding did not preclude defendants from offering testimony about their relevant behavioral tendencies and limited its exclusion of evidence to that which concerns a defendant's actual capacity to form a certain mental state. Id. at 544, 931 P.3d at 1054.