Several Pulse regulars have come forward in the days since the shooting, claiming to have seen Mateen at the club or to have been contacted by him on the gay dating apps Grindr, Jack’d and Adam4Adam.

On Tuesday, Univision aired a report in which “Miguel,” a man wearing a disguise to conceal his identity, alleged he had sex with Mateen after meeting him on the gay dating app, Grindr. He said Mateen had sex with other men too, including a threesome with a Puerto Rican who allegedly told Mateen, after having had unprotected sex with him, that he was HIV positive.

But investigators do not consider the man’s account credible, according to one senior law enforcement official with access to the investigation.

In seeking to verify the reports, federal agents have culled Mateen’s electronic devices, including a laptop computer and cellphone, as well as electronic communications of those who made the claims, law enforcement officials said.