Omar Mateen, 29, carried out the shooting at Pulse, a popular gay nightclub, on June 12.
Mateen, who was killed at the scene, was married with a young son. He told police that he was acting in allegiance to ISIS.
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Several regulars at Pulse have come forward saying that they had seen Mateen at the club before and that he had regularly used the gay dating apps Grindr and Jack'd.
A man, identified only as "Miguel," told Univision that he and Mateen were "friends with benefits," and that they had met up between 15 and 20 times.
FBI agents have looked into Mateen's laptop and cellphone, but have so far found nothing indicating that Mateen was gay, reports the Los Angeles Times.
The FBI will continue to investigate Mateen, but believes that the men who claimed that Mateen was gay may have not been credible.