The brother of Vegas shooter Stephen Paddock bragged about being related to him after the attack ... and that's how he got busted for child porn.
Law enforcement sources tell TMZ ... the day after Stephen Paddock slaughtered 58 people, his brother Bruce bragged to folks at the assisted living facility, where he was staying, that Stephen was his brother.
We're told someone on the staff checked Bruce's file at the facility and, sure enough, Stephen Paddock was listed as Bruce's emergency contact. The staffer called the LAPD, assuming cops would be interested in speaking to Bruce.
Sources say as cops and the FBI started digging for info on Bruce, an active search warrant in a child porn case popped up ... leading to his arrest after cops pinpointed his location.
TMZ broke the story ... Bruce maniacally evaded arrest from cops for years -- from changing his appearance to setting up booby traps.