The ex-US Navy reservist who killed 12 people and wounded eight at a Washington DC Navy installation had received treatment for mental health issues, US media have reported.
Aaron Alexis, 34, was treated for paranoia, insomnia and hearing voices, the Associated Press reported.
A contractor for the Navy, he had a valid pass for the secure site at the Washington Navy Yard, authorities said.
On Tuesday, authorities said they believed Alexis had acted alone and that all victims – ranging in age from 46 to 73 – had been identified.
Authorities have revealed no motive for the attack, and have begun combing the US for hints about Alexis’ past.