Within the craze there will be a motivation based on self interest one way or another.Exactly. Crazy people don't do things for NO reason, they do things for CRAZY reasons!
I think your hypothesis is well put and applies to serial killers and many of those who murder strangers for no apparent reason.
In this case MOO boy wants girl, girl wants no part of boy, maybe unaware boy exists except as a pesty request on IG.
Boy tortured by his own inadequacies projects rejection into a “system” of girls who conspire to keep worthy men such as himself from becoming boyfriends.
The viewpoint that he is being intentionally hurt and his desire for the girl join up for a strong impulse to end the situation. Decides on a “victory” for himself by using his superior force.
Oops, lots of folks in the way, regrettable but not a big deal. Boy is crazy (fractured) feels he won by ending her.