is that not enough to prove insanity, on the premise that he believes in god.
His lack of remorse is a symptom of him being a sociopath, sure- but sociopaths are generally considered to be overall sane. Sanity is based on whether the person knows right from wrong. Sociopaths generally know right from wrong, they just don't care as much, because they dont feel emotions as strongly as a normal healthy person will. Some sociopaths are totally non emotional, and do not know right from wrong, and those ones are obviously insane.
He might even be an antisocial personality disordered person, because he seems to feel as though he is above the law- which is textbook behavior for an antisocial PD person.
This guy knew that what he was doing was wrong ,in any event, so no he is definitely not insane, by court standards, even if he has a mental illness.