That should be good to get any Moslem off of any violence or theft charge. Moslems cant know that any of that stuff is wrong because their holy book instructs them that it is right and mandated.
Muslims know exactly what they’re doing when they kill because they wouldn’t want the same done to them. The Koran teaches them to kill and be killed for Islam.
What it does besides making every Muslim an empowered vigilante is to guarantee a win-win regardless of outcome. Victory on Earth or “Jannah” (paradise) afterward.
No insanity defense is therefore acceptable for Muslims who kill those whom they regard as “infidels”.
As for method of execution, he should be hanged from a cherry picker with his toes touching the ground. Let him think about it for a while.