Sorry if this isn't the right subforum for this topic, but it's a hard one to place. This is a neat in-depth look at the Parkland shooter, who tried to feign insanity. I'm not trying to put forth any political argument or anything with this, but sharing it for the education and enjoyment of all. So, enjoy!
It doesn't matter if they're "insane", all that matters if they were "insane enough" at the time of the offense to be unaware of what they were doing.
You could easily make the argument that you would have to be inherently insane to do what it was that he did that is not the actions of a sane person
Having worked with the "insane" (for lack of a better "term") I've never bought into the "didn't KNOW what they were doing was wrong" argument....they know, they just don't care...let's try another verdict, "Guilty, BY REASON of insanity"!
I think evil is a type of insanity, but legally and morally it's not "the same" as being unaware of your actions.
Evil and insanity are both vague, non-scientific, non-clinical terms, anyway. There are various pathologies that can make someone basically "not care" about killing or doing other things that would generally be considered "evil." You get an example of a genuinely pathological murderer who shows no remorse starting at around four minutes into the video, which is provided for comparison and contrast, while the main subject of the video is featured starting at around the 10:30 mark and beyond.