Fisher Stevens -- Grand Canyon Squirrel Kicker Can't Hide

The cold-hearted bastard who kicked a squirrel off a Grand Canyon ledge will absolutely be hunted down because he pissed off the wrong people ... according to actor Fisher Stevens.

Fisher was outside BOA Steakhouse last night when we told him about the insane story -- 2 French-speaking men recently used bread crumbs to lure the squirrel, and then one of them punted the poor animal into the air. Video of the crime went viral.

Now the suspects have law enforcement on their asses, but Fisher thinks the key to their capture might be PETA's $15,000 bounty.

Fisher's an animal rights advocate himself -- he won the Oscar for "The Cove" -- and thinks the killers won't get away with it while PETA's on the case.