Yes I was wondering about who he listened to or what groups he may have been involved in or what if any drugs he may have been taking. Seems odd that a guy who was described as nice and quiet just goes off like that.
If I didn’t know better I would think someone has been in his head telling him to do it. It reminds me of the movie
“The Kiling Room”
He was at just the right age when schizophrenia often strikes. Late teens, early twenties. Wonder if it might have been that?