US investigators have questioned the wife of the gunman who killed 49 people at a gay nightclub in Orlando, the FBI has said.
Furthermore a law enforcement source has told Reuters said she could face criminal charges if there is evidence of any wrongdoing.
Omar Mateen's wife, Noor Salman, knew of his plans for what became the deadliest mass shooting in modern US history, said the source, who has been briefed on the matter.
The FBI held a press conference on the investigation this evening.
"With respect to the wife, I can tell you that is only one of many interviews that we have done and will continue to do in this investigation," FBI Special Agent Ron Hopper told reporters. "I cannot comment on the outcome or the outcome of that investigation."
The FBI wanted to hear from anyone who had contact or information about the gunman, Mr Hopper said, adding that it had advised gay nightclubs in the area to be on alert.
US Attorney Lee Bentley declined to say whether Ms Salman or any other associate of Mateen's could face criminal charges, saying there was no timetable for such a decision.
"It appears she had some knowledge of what was going on," said US Senator Angus King, a member of the Senate Intelligence Committee, which received a briefing on the attack yesterday.
"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," Mr King told CNN.
Mateen, who was shot dead by police after a three-hour standoff at the Pulse club in the early hours of Sunday morning, called 911 during his shooting spree to profess allegiance to various militant Islamist groups.
Federal investigators have said he was likely self-radicalised and there was no evidence that he received any instruction or aid from outside groups such as the so-called Islamic State militant group.
Mateen, 29, was a US citizen, born in New York of Afghan immigrant parents.
"He appears to have been an angry, disturbed, unstable young man who became radicalised," President Barack Obama told reporters after a meeting of the White House National Security Council.
During his attack, Mateen systematically made his way through the packed club shooting people who were already down, apparently to ensure they were dead, said Angel Colon, a wounded survivor.
"I look over and he shoots the girl next to me and I was just there laying down and thinking: 'I'm next, I'm dead,'" he said.
Mateen shot him twice more, one bullet apparently aimed for Mr Colon's head striking his hand, and another hitting his hip, Mr Colon said at Orlando Regional Medical Center, where he is one of 27 survivors being treated.
FoxNews.com, citing an FBI source, said prosecutors were seeking to charge Mateen's wife as an accessory to 49 counts of murder and 53 counts of attempted murder and failure to notify law enforcement about the pending attack and lying to federal agents.
NBC News said Ms Salman told federal agents she tried to talk her husband out of carrying out the attack.
But she also told the FBI she once drove him to the Pulse nightclub because he wanted to scope it out, the network said.
A former wife of Mateen, who was a security guard, has said he was mentally unstable and beat her.
The ex-spouse, Sitora Yusufiy, said she fled their home after four months of marriage.
Ms Salman's mother, Ekbal Zahi Salman, lives in a middle-class neighbourhood of the suburban town of Rodeo, California. A neighbour said Noor Salman only visited her mother once after she married Mateen.
He said he had spoken to Noor Salman's mother after the Orlando attack. "She was crying, weeping."
Taoiseach Enda Kenny, meanwhile, has signed a book of condolences for the victims at the Mansion House in Dublin.
The Taoiseach's message to the people of #Orlando , America and the LGBT Community pic.twitter.com/D3VFFbGNtl
— Micheal Mac Suibhne (@MicMacSuibh) June 15, 2016
