When will a court order a competency hearing for a defendant with mental health issues?

Pate v. Robinson , supra , 383 U.S. 375, 86 S.Ct. 836 ( Pate ), the high court made clear that when substantial evidence of incompetence otherwise exists, a competency hearing is required even though the defendant may display "mental alertness and understanding" in his colloquies with the trial judge. ( Id. at p. 385, 86 S.Ct. 836.) The court explained that while the defendants in-court behavior "might be relevant to the ultimate decision as to his sanity, it cannot be relied upon to dispense with a hearing on that very issue." ( Id. at p. 386, 86 S.Ct. 836.)

This court has followed the same principle: When faced with conflicting evidence regarding competence, the trial courts role under Penal Code section 1368 is only to decide whether the evidence of incompetence is substantial, not to resolve the conflict. Resolution must await expert examination and the opportunity for a full evidentiary hearing. ( People v. Lightsey (2012) 54 Cal.4th 668, 703704, 143 Cal.Rptr.3d 589, 279 P.3d 1072 ; People v. Pennington , supra , 66 Cal.2d at p. 518, 58 Cal.Rptr. 374, 426 P.2d 942.) Had the issue of defendants competence been tried to the court under Penal Code section 1369, the trial court might legitimately have weighed defendants demeanor and the nature of his responses to the courts questioning against the experts reports and other available evidence relating to his condition. But in the face of substantial evidence raising a doubt about defendants competence, defendants demeanor and responses supplied no basis for dispensing with further inquiry.