Here is how it usually works: he exhibits a pathological focus on the self, which likely comes from childhood trauma. He also lacks empathy or conscience in ways that reveal an undeveloped humanity.... https://twitter.com/GallowayToby/status/1249775203900706816
... These by themselves do not make one criminal, but when one has criminal intent, unspeakable evil can result. Hence, there is criminal responsibility, which combines with pathology to become more dangerous.
The presence of “insanity” does not lead to an insanity defense, in fact it seldom does. Free will largely persists even in the most debilitated individuals. And most dangerous behavior is driven by criminal-mindedness, very little by mental illness.