In addition to associating with Marcus Dwayne Robertson, a known longtime FBI informant with links to the CIA, and working for a security company that carries out clandestine operations for the CIA, the FBI introduced suspected Orlando shooter and "known quantity" Omar Mateen to informants.

From the New York Daily News on Monday:

FBI investigators investigated Mateen, who was born in New York, for 10 months. They introduced him to confidential informants, spied on his communications and followed him. They also interviewed him twice.

The alleged Boston Marathon bomber, Tamerlan Tsarnaev, was also approached by the FBI and asked to work as an informant.