I would do everything I can with the police. The odds are that this guy will get picked up for something else, and if it’s similar, they might call you in to look at a picture, at which point they can add the charge. It’s not like he doesn’t deserve the extra time locked off the streets.
Cheesesteak, I admire your willingness to go out of your way to help a stranger. Do you think the stalker creep was mentally ill, or just really pissed off about something?
Bah, what’s a punch in the face compared to all that good karma? Just keep your nut kickin’ leg ready in case this guy shows up again. 
Good job Cheesesteak, you did what ya shoulda done. Next time though, duck. 
I’ll definitely duck next time! I think this guy was either drunk, on something illegal, or off something legal, there was something just too off about him for this to be his normal state.
I figure I won’t hear from the NYPD again about this, my description was too vague for them to just pick him up, or call me about it after the fact if he does get picked up. As far as they’re concerned, he’s a somewhat older, medium sized black man with a beard who “harassed” someone, not gonna hit their radar.
Just keep a careful eye out for a while - he could be looking for a little payback for whatever offense he thinks you’ve committed by preventing whatever he had planned for the woman you helped protect. A little sensible paranoia may be called for in the short term.
You did a good, honorable thing. I’d shake your hand if we weren’t half a continent apart.