The navy yard shooting accused Aaron Alexis had a history of mental illness and run-ins with the law that should have denied him access to military bases such the Washington base, where he killed 12 people on Monday.
But he had an all-access pass that allowed him to walk into Building 197, position himself above an atrium and shoot people with a shotgun purchased just a week ago.
He was shot dead in an exchange of fire with the police.
Vishnu Pandit, a 61-year-old Indian-American, was among those killed. Pandit came to the US from Mumbai in 1974 to study engineering, according to his friends. A month before the shooting, Alexis had called police to a hotel he was staying in Newport, Rhode Islands complaining of hearing voices and people following him.
He told the police a person with whom he had an argument in Virginia had sent three people to follow him and “keep him awake by talking to him and sending vibrations into his body”.
Alexis said, according to the police report, he believed these people were using some sort of a “microwave machine” to send vibrations into his body to prevent him from sleeping.
President Barack Obama and a growing number of Americans are now pushing for laws to prevent criminals and those with mental illness from buying guns.
Another man with a history of mental illness, Adam Lanza, gunned down 20 first-grade children and six adults in an elementary school in Connecticut last November. Alexis had a criminal track record too, with at least three arrests across three states for offenses ranging from traffic violation to shooting tires of a car in anger over imagined slight.
There was also a pattern of behaviour at work, now being called red flag, that should have earned him a general discharge, denying him security clearance that he had.