By Ian Simpson
WASHINGTON, Sept 19 (Reuters) - Thousands of workers streamed back into the Washington Navy Yard on Thursday, three days after a former reservist working at the site as a contractor opened fire with a shotgun on a cafeteria full of workers eating breakfast, killing 12 people.
The sprawling, walled complex, which covers about 16 blocks of the U.S. capital, had been closed to all but essential personnel and those involved in the investigation into why 34-year-old Aaron Alexis, who died in a gun battle with police, mounted his attack.
A steady stream of workers entered the Yard through a security gate, swiping cards at a turnstile. A Navy guard checked IDs.
"To be productive we can't dwell on the past," said Justin Hoffman, 27, a civilian Navy IT worker, who had just emerged from the base and said security was heightened, with more guards visible.
Angelo Esposito, 60, an IT worker in the engine program, said the return to a workday routine felt "weird." "I used to think of this as a safe place," Esposito said.
Eric Schechtman, 56, a software engineer, said he had never anticipated a mass shooting at the Yard, where he has worked five years and which is less than two miles from the U.S. Capitol. "You hear about mass shootings, they're usually somewhere else and they happen to someone else, far away," he said.
Alexis, a U.S. Navy Reserves veteran, entered the base on Monday with a security clearance that allowed him onto military facilities to work as an information technology contractor.
His credentials were still valid, although Rhode Island police had warned the Navy in August that Alexis had reported "hearing voices" and said he believed people were following him and "sending vibrations into his body," according to a Newport police report.
A senior Navy official said on Thursday the service was reviewing why that report had not been shared more widely.
"We don't have any indications that the reports from the Newport police went any higher than the local base security officers there at Newport," Rear Admiral John Kirby, Navy chief of information told CNN.
"We're taking a hard look at that as well to see why that report didn't go any higher and what should have been done better to make authorities at a higher level than their base security aware of it," Kirby said.
The attack was the second mass shooting on a military base inside the United States in four years. In November 2009, a gunman killed 13 people and wounded 32 at the Fort Hood Army base in Texas.
That shooter, Major Nidal Hasan, said the attack was intended as retaliation for U.S. wars in the Muslim world. Last month a military jury sentenced him to death.
Both incidents shed light on a security conditions within military installations. Military personnel other than security forces are typically prohibited from carrying firearms while on bases, leaving them vulnerable to attacks of the kind seen in Washington and Fort Hood.
After Monday's attack Defense Secretary Chuck Hagel ordered a worldwide review of security at U.S. military installations.
Washington Navy Yards, on the Anacostia River which is a tributary of the Potomac, was established in 1799 as a shipbuilding site and a base for defending the city. The complex houses the Naval Sea Systems Command, as well as a human resources operation for Navy civilian workers and a museum and art gallery. (Additional reporting by Vicki Allen; Writing by Scott Malone; Editing by Barbara Goldberg and David Storey)