I remember something like: It was a movie that a boy kinda hang out with a killer. And in one of the scenes, the “killer” stops his car near another car and tell the boy to memorize the car plate.
Also iirc there’s a scene of this same boy digging his own grave right before the “killer” kill him.
Acolytes (2008)?
https://www.imdb.com/title/tt0902952/?ref_=fn_al_tt_1