The FBI says agents are searching a Phoenix apartment as part of the investigation into the deadly shooting outside a suburban Dallas venue hosting a provocative contest for Prophet Muhammad cartoons.

FBI spokesman Perryn Collier on Monday confirmed the Phoenix residence is being searched for indications of what prompted the shooting Sunday that left two gunmen dead and a security officer wounded outside a center in Garland.

ABC News cites a senior FBI official in reporting that one of the gunmen, a resident of the Phoenix apartment, was known to authorities and was the subject of an investigation. The ABC report says the man was convicted five years ago of lying to federal agents about plans to travel to Africa, in an apparent attempt to join a terror group there.