Orlando nightclub gunman Omar Mateen told police during negotiations that he would strap explosives to four hostages and put them in the corners of the building, the city's mayor revealed, as authorities faced criticisms over their decision to send a SWAT team into the building and a delay in removing the dead.
The New York Times quoted Mr Buddy Dyer as saying that over the course of several hours after Omar, 29, attacked the Pulse nightclub and took hostages on Sunday, he told police negotiators that he planned to strap bombs to four people.
In phone calls and text messages to 911 operators, friends and family members, he also warned of explosives, according to people trapped inside the club.
"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," NYT quoted Mr Dyer as saying.
The concern that explosives might be at play grew after Mateen was killed, the mayor added.
"When the shooter was killed, you could see a battery pack right next to him, which would indicate to us that there's a detonator of some sort," he was quoted as saying.
"There was also a bag near his body, so you would logically lead to the conclusion that the bag contained explosives and he had some type of detonator that could have been a pressure detonator that was under the body."
Because of this concern over explosives, authorities had to wait several hours before the building was cleared, he added.
Mateen's assault on Pulse nightclub left 49 people dead and 53 wounded in the worst mass shooting in US history. He was shot dead by police SWAT team members after a three-hour standoff.
In his call to 911 operators during his rampage, he professed allegiance to various militant Islamist groups., including the Islamic State in Iraq and Syria.
FBI investigators have questioned the wife of Omar and a law enforcement source said she could face criminal charges if there is evidence of any wrongdoing, according to Reuters news agency.
US Senator Angus King, a member of the Senate Intelligence Committee, which received a briefing on the investigation into Sunday’s massacre, told CNN it appeared that Noor Salman had “some knowledge” of what was going on.
“She definitely is, I guess you would say, a person of interest right now and appears to be cooperating and can provide us with some important information,” he said.
She was with Omar when he cased possible targets in the past two months, including the Disney World resort in April, a shopping complex called Disney Springs and the Pulse nightclub in early June, CNN and NBC reported.
Federal investigators have said Omar was likely self-radicalised and there was no evidence he received any help or instructions from outside groups such as ISIS.
He was a US citizen born in New York of Afghan immigrant parents and worked as a security guard.
“He appears to have been an angry, disturbed, unstable young man who became radicalised,” President Barack Obama told reporters.