Maybe only his psychiatrist would know. Maybe he studied the evil and depravity that is mohammadanism so deeply and thoroughly it tipped his already damaged mind right over the edge.
Maybe he was under the influence of a hallucinatory substance, maybe he was hypnotized...
Did he have a psychiatrist? I doubt it. And see, here you go with “over the edge”. The edge of what? This is act is entirely unprecedented, except as an expression of Jihad. So why wasn’t it Jihad? ... well, he was nuts ... not enough for me.