Barron Hilton -- Cops ID Face Puncher ... And Now They Want Answers

The guy who's being accused of punching the crap out of Barron Hilton's face this week has been ID'd by police ... and now cops are on a mission to crack the case ... TMZ has learned.

Law enforcement sources tell us ... the puncher has been identified based on witness testimony as New York resident Ray LeMoine -- and now they want his side of the story.

We're told officers attempted to interview Ray yesterday outside the house where he allegedly beat up Paris Hilton's little bro on Friday ... but nobody was home.

As for Lindsay Lohan -- who's being accused of orchestrating the attack -- our sources say they tried to question LiLo yesterday at her new hotel ... but she was M.I.A. both times.