I'm sure they confronted him - why do you think he was hiding in the stall?
When the police got there, that's why; "he was found". He may have known some commotion was going on - duh! The kid screamed.
I don't know, maybe some1 did go in and catch him - or at least, corner him while at arm's length. The stories aren't explicist. But it sounded like maybe the kid got away while screaming. So of course the dude would be afraid to leave, cuz screaming drew attention to the bathroom. How would he escape?