(NBC News) In the wake of yesterday's deadly rampage at the Washington Navy Yard, the FBI today confirmed there was only one shooter.
They say 34 year old Aaron Alexis acted alone and had the proper security pass to get on the base.
Now, much of the focus of the investigation is centered on that pass.
The fact that Alexis was cleared onto this base yesterday, apparently concealing his shotgun, is prompting hard questions about why he was able to keep his secret-level security clearance.
Some workers returned to the navy yard, calling yesterday a nightmare.
"I'm glad to be alive, you know everyone's glad to be alive. You never can tell what's gonna happen when you come to work and life in general," said one person who works at the Navy Yard.
Investigators today searched a hotel near the navy yard used by Alexis.
The FBI also confirmed today that Alexis acted by himself.
"This type of lone wolf actor is very difficult to identify unless they send up red flags on a repeatable basis," said NBC National Security Analyst Roger Cressey.
But Alexis did.
Law enforcement said he was treated by the Veterans' Administration for paranoia.
Police near the Navy base in Newport, Virginia said Alexis told them last month he was hearing voices.
He also had run-ins with police after firing a gun in 2004 and 2010.
And in 2011 the navy discharged him early for insubordination.
But Alexis never lost the security clearance he'd been granted in 2008.
They say he used that pass to gain access to the building and open fire with a shotgun, not an assault rifle.
Today Defense Secretary Chuck Hagel placed a wreath to honor the dead and injured.
The republican chairman of the House Armed Services Committee says a yearlong investigation suggests the Navy implemented an unproven security system to try to cut costs.
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