Adam your version of Jeremy is quite an enigma
Clever enough to plan two shots
But stupid enough to tell his girlfriend
Clever enough to plan a call from his father
but stupid enough not to wait a while and make it a proper emergency call rather than dilly dally
Clever enough to LOCK a window behind him
but stupid enough to tell the police he could get in and out of the house
He was such a namby pamby he could not shoot rabbits
but could shoot his whole family and stand calmly next to police
He was not speaking to his mother ( according to you )
But he was happy to go round for supper.
Clever enough to totally dispose of any forensic evidence
But dumb enough to leave the silencer with a Blob of blood .
You are weaving an intricate personality .
And before you say anything there is a source that he was thoroughly tested face to face ( not by someone who had never met him , and he was not a psychopath.