what movie? killer "blends in", goes unnoticed until somebody pays attention

at least that's what I can remember - it was quite interesting.

the killer's characteristic was that he looked like "anybody" so he would go unnoticed whenever he committed a crime. can't remember how he is busted, some girl might fall in love with him so he is noticed...or something.

watched this movie a while ago, and I've been trying to remember the title but have not been able to. all google searches have failed.

PLEASE HELP!!!