Aaron Alexis, 34, the former Navy reservist who shot dead 12 people at a US naval yard before he was killed by police, was reported to be suffering from serious mental health issues.
Alexis, who was a defense contractor at the base, had been treated since August by the Veterans Administration for his mental problems, officials told AP news agency.
According to Sky News, he had been hearing voices in his head for some time and was suffering from paranoia and a sleep disorder.
Despite previous confrontations with the law, he had access to the highly secure Navy Yard as a defense contractor, and the F.B.I. say that he used a valid pass to enter the base to carry out the shooting.
The Washington Navy Yard is protected by armed guards and metal detectors, and employees have to show their IDs at doors and gates. However, Alexis was carrying three weapons – an AR-15 assault rifle, a shotgun, and a handgun.
David Stevens, who was on the third floor of a building when the shooting began, told The Washington Post: “It’s unbelievable that someone could get a rifle in there.”
Alexis had been a full-time Navy reservist from 2007 to early 2011, but his military service was marked by disciplinary problems. Alexis was discharged from the Navy in 2011.
Although he was discharged for misconduct, he still received two medals during his service which are issued to large numbers of service members who served since the 9/11 attacks.
At the time of the shooting spree, Alexis was employed as an IT subcontractor and was working on a Hewlett-Packard contract to upgrade equipment for an intranet network used by the US Marine Corps and Navy.
It is not known if the military or HP had been aware of Alexis’ problems with the law before he was hired for the job.
The shooting set off a massive show of force as police and federal agents descended on the Navy Yard,which less than two miles from the Capitol.
Outside the Alexis family home in Brooklyn, Alexis’s brother-in-law, Anthony Little, said the family were distraught.
“Their hearts are going out more to the victims who got hurt because you know it’s more lives lost and we don’t need that right now,” Mr Little said.
Aaron Alexis is no longer hearing voices, so we can only speculate as to what those voices were telling him to do.