FBI agents have questioned a member of the Florida mosque attended by Omar Mateen, whoshot 49 people to death at a gay nightclub in Orlando, as new information showed the killer exhibited chronic behavioural problems during his youth.
Academic records obtained by Reuters showing Mateen was frequently suspended as a student — at least twice for fighting before he was transferred to a special high school for potential drop-outs — added to a disturbing portrait of the gunman who committed the deadliest mass shooting in modern US history.
The 29-year-old private security guard, who was shot dead by police at the end of the June 12 massacre, has been described by his first wife — whom he divorced after a brief marriage — as an abusive, mentally disturbed man with a violent temper.
Others who knew him recalled Mateen, a US citizen and Florida resident born in New York to Afghan immigrants, as a quiet, socially-awkward individual who kept largely to himself.
The FBI has acknowledged interviewing Mateen in 2013 and 2014 for suspected ties to Islamist militant groups but concluded he posed no threat.
Still, evidence in the Orlando case points to a crime at least inspired by extremist ideology.
Authorities have said Mateen paused a number of times during his three-hour siege at the Pulse nightclub to place cell phone calls to emergency 911 dispatchers and to post internet messages professing support for various Islamist militant groups.
Nevertheless, Mateen appears to have been "self-radicalised" and acting without any direction from outside networks, although his second wife Noor Salman had known of his plans to carry out the attack, US officials have said.
A federal grand jury was convened earlier in the week to decide whether to charge Ms Salman.