Jeremy would NOT have been aware at the time that Sheila would have been capable of killing,and because his father had rang to say that she had a gun wouldn't have meant,to him,that she was about to use it on " all " of them. He didn't use her " madness " as an excuse !
No,no,no,Jeremy WASN'T the killer ! Mothers who kill !! It was virtually unheard of in the 80's.