The police were told by Mateen that he placed explosives in the building and strapped on devices on four of the hostages and placed them at each corner of the building.
“We had a lot of information from the inside and they independently were saying yes, the bomber is about to put on an explosive vest,” Orlando Mayor Buddy Dyer said.
So far, investigators have not found any evidence that Mr. Mateen, 29, had explosives, senior law enforcement officials said Wednesday. His rampage with an assault rifle and a handgun left 49 people dead and 53 wounded, the worst mass shooting in United States history, and he died in a shootout with law enforcement officers.
Investigators continued looking into whether his wife, Noor Zahi Salman, knew what he had planned, but at a news conference, officials deflected questions about possible criminal charges against her.
“I’m not going to speculate with respect to any charges that might be brought,” said A. Lee Bentley III, the United States attorney for the Middle District of Florida. “We’re not sure what charges will be brought, or if charges will be brought.”
Ms. Salman has told F.B.I. investigators that she had tried to talk her husband out of some kind of attack, according to senior law enforcement officials. But she also told them that she had gone with him to buy ammunition, and that she had once driven him to Pulse, they said.