Mr. Comey said the 34-year-old finished his 12-person killing spree with a Beretta semi-automatic pistol he took after fatally shooting a security guard.
“It appears to me that he was wandering the halls and hunting for people to shoot,” said Mr. Comey.
The new details gleaned from video evidence emerged as the Navy Yard reopened for normal operations Thursday and questions mounted over why the Navy information technology contractor was able to obtain secret clearance despite an arrest record, a history of mental illness and a difficult military career.
“We’re attempting to understand as best we can his life up until the moment of that shooting, which would include whether there were issues related to work,” Mr. Comey said.
Mr. Comey said Alexis entered the Navy Yard in a vehicle, parked in a deck across from Building 197, entered carrying a bag, went into a fourth-floor bathroom and came out shooting in no discernible pattern. He then went down to the lobby and fatally shot a security guard.
After killing the guard, Alexis ran out of shotgun ammunition and continued shooting workers with the seized pistol, Mr. Comey said, until officers engaged him in an exchange of gunfire that ended in his death.
As the FBI continues its investigation at the crime scene, joined by the Navy, U.S. Park Police and the Metropolitan Police Department, which had an officer wounded in the shootout, the Bureau of Alcohol, Tobacco, Firearms and Explosives is pursuing leads that could include whether Alexis purchased other guns prior to his rampage, according to ATF Agent Tim Graden.
Meanwhile, U.S. Capitol Police Chief Kim Dine has ordered a separate investigation following revelations, first reported by WUSA-TV (Channel 9), that a commander ordered officers who responded to the shooting to leave the scene.
Officers with the Capitol Police’s Continuing Emergency Response Team told union leaders that they arrived at the Navy Yard “fully deployed and with a sniper,” but were instructed to return to Capitol Hill.
Capitol Police Labor Committee Chairman Jim Konczos told The Washington Times that because commanders report to both chambers of Congress, confusion resulted when orders were issued to “lock down” the Senate and “shelter in place” — but not the House.
It is unclear whether the order to “shelter in place” at the Senate triggered the order for the team to return to the Hill.
Senate Sergeant-at-Arms Terrance W. Gainer, chairman of the Capitol Police’s board, did not return calls for comment.
“We’re disappointed,” Mr. Konczos said, expressing regard for the various agencies that deployed Monday and are continuing to investigate. “We should’ve been allowed to act in the capacity we’ve been trained to do.”
Separately, Congress has asked the inspector general at the U.S. Office of Personnel Management to investigate how a clearance was awarded to Alexis. Just weeks ago, the Navy had warned employees under its new “insider threat” program that all personnel were responsible for reporting suspicious activity that could lead to terrorism, espionage or “kinetic actions” — a military euphemism for violence.
Defense Secretary Chuck Hagel has ordered a sweeping review of all military security and employee screening programs.
• This article is based in part on wire service reports.