Omar Mateen was the son of an Afghan immigrant who had a talk show in the United States.
James Comey said the man, who has been identified as 29-year-old Omar Mateen, also spoke with a 911 operator three times during the deadly event. At one point, Comey said, he pledged loyalty on the call to the head of the Islamic State group.
READ THE FULL LIST OF VICTIMS.
Comey's remarks offered further detail on the shootings that left 49 victims dead and more than 50 hurt, making it the deadliest mass shooting in modern U.S. history. Mateen died in a gun battle with police.
President Barack Obama said Monday the killer was inspired by extremist information over the internet, calling it an apparent example of the "homegrown extremism" that U.S. officials have been worrying about for years.
Mateen had twice come to the FBI's attention before Sunday's shooting, the FBI said. It investigated him for 10 months, beginning in May 2013, because he had made "inflammatory and contradictory" statements about ties to terrorist groups that caught his coworkers' attention.
Mateen was working at the time as a contract security guard at a local courthouse. He has held a Florida license to be an armed security officer since at least 2011, state records show.
Mateen had told coworkers "he hoped that law enforcement would raid his apartment and assault his wife and child so that he could martyr himself," Comey said.
The FBI's Miami field office opened a preliminary investigation to determine whether Mateen was "possibly a terrorist." The FBI began introducing him to confidential sources, following him and reviewing some details of his communications.
The FBI director also said that Mateen at the time claimed family connections to al-Qaida and was a member of Hezbollah, which Comey said "is a Shia terrorist organization that is a bitter enemy of the so-called Islamic State."