JM may have not thought about all of the things we are thinking that could have happened that night but I imagine he has gone over some type of plan in his mind a time or two. I have yet to hear anywhere if someone has found something that triggers him in the fall time. "Back to school" rapist/killer/abductor. Maybe he is mad because he never got to finish college cause he was kicked out? Maybe he was getting more and more mad as time passed (being 32 now and never finished college) and has made it really tough on LE to be able to ID remains.
Maybe there are more young girls who are drunk/vulnerable available once school starts back up.
I see it just the same as deer hunting season. Deer hunters go during hunting season, which is set at a time when conditions are right for plentiful deer.
JM hunts young vulnerable women. Fall back-to-school, with plentiful parties and alcohol and new coeds wandering around. 'Tis the season. IMO.