US federal investigators believe the Florida shooter, Omar Mateen, was likely self-radicalised and there was no evidence that he received any instruction or aid from outside groups such as Islamic State.  Mateen, who was shot dead by police after a three-hour stand-off at the Pulse club early on Sunday, called 911 during his shooting spree to profess allegiance to various militant Islamist groups.  The FBI interviewed Orlando, Florida, shooter Omar Mateen when it was investigating Moner Mohammad Abu-Salha, an American suicide bomber in Syria, because they were casual acquaintances who attended the same mosque, the head of the Senate intelligence committee says.  "Our understanding is the only reason he was interviewed at a later date was not that he was the subject of additional concerns: They were trying to connect the dots on the suicide bomber," Republican Senator Richard Burr told reporters on Tuesday.  "It just so happened that they'd gone to the same mosque and it was determined that they were casual acquaintances but there was not a connection there that they needed to look at," he said.  The revelation came as law enforcement sources said Mateen's wife Noor Salman, could be charged in connection with the deadliest mass shooting in modern US history as early as Wednesday.  "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.  NBC News said 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.  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 rampage, 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 Colon's head striking his hand, and another hitting his hip, Colon said at Orlando Regional Medical Center, where he is one of 27 survivors being treated  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.  Mateen made 911 calls from the club in which he pledged loyalty to the leader of IS, Abu Bakr al-Baghdadi.  He also claimed solidarity with the ethnic Chechen brothers who carried out the 2013 Boston Marathon bombing and with a Palestinian-American who became a suicide bomber in Syria for al-Qaeda offshoot the Nusra Front, authorities said.  "We could hear him talking to 911 saying that the reason why he's doing this is because he wants America to stop bombing his country. From that conversation from 911 he pledges allegiance to ISIS," said Patience Carter, 20, who was trapped in a bathroom stall at the nightclub as Mateen prowled outside.  One official said investigators believe Mateen browsed militant Islamist material on the internet for two years or more before the shootings.  Soon after the attack, Mateen's father indicated that his son had harboured strong anti-gay feelings. He recounted an incident when his son became angry when he saw two men kissing in Miami while out with his wife and son.  US officials were investigating media reports that Mateen may have been gay but not openly so, and questioning whether that could have driven his attack, according to two people who have been briefed regularly on the investigation and requested anonymity to discuss it.
A US official has suggested the gay nightclub shooting may have been a "self-hate crime" amid reports the gunman may have been secretly gay himself.