“If he really was an innocent boy unnerved by a man following him in a truck, it would make a LOT of sense to leave the road and take to the shortcut”. . .AND call the police to report some lunatic following him.
No one with innocent intent heads into the dark. A young man with good intentions would have stayed in sight and in the light on the street or knocked on a door, not hidden in the shadows behind the houses.
That’s one thing that bothers me. Why would tm call the girlfriend and not the police?
Or take that short cut to quickly go back to the apartment.