Omar Mateen, told the police by phone that he would strap explosives to four hostages

ORLANDO, Fla. — Amid the massacre at a gay nightclub here, while the gunman held dozens of people hostage, the police got word from multiple sources that the killer had booby-trapped himself, hostages and the building with explosives, Orlando’s mayor said on Wednesday.

Holed up in Pulse nightclub early Sunday, the gunman, Omar Mateen, told the police by phone that he would strap explosives to four hostages and place them strategically in the corners of the building, Mayor Buddy Dyer told reporters. People trapped inside made panicked calls and text messages to 911 operators, friends and family members, also warning that Mr. Mateen was talking about bombs, he said.

“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,” Mr. Dyer said.

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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.