The Orlando gunman went to the Pulse nightclub earlier Saturday night and then left before returning to carry out his attack as the gay club prepared to close early Sunday morning, law enforcement officials say.

The gunman paid the entry fee, obtained a wrist band, and entered the club, the officials said.

Investigators believe he may have been checking the club security.

Surveillance video, cell phone tracking along with witness interviews have helped the FBI to build a timeline of his whereabouts on the night of the attack.

But they are still working to determine what he was doing for a two-hour period between when he left the club and returned.