I mean obviously this guy deserves to be caught, but the last thing the city needs is for busy bodies to be laying beat downs to people in the streets. Yes if this person is actively assaulting someone or looking in a window exposing himself, etc by all means stomp his ass. I just can see someone totally innocent that looks vaguely like the suspect and perceived to be acting suspicious and some vigilante that watched the movie Kick Ass comes along and mobs them.

Leave it to the cops. Observe and report til they get there. Give a good description and accurate location. I'm sure they want to get this guy just as badly. The cops also have protections from civil liability and prosecution where regular citizens do not. You can be sued and possibly face charges for false arrest or injury.