The picture emerging of the dead gunman in Monday's rampage at the Washington Navy Yard is a study in contrasts, one of a man who practiced languages and meditated, and another of a cold-blooded killer.
The gunman was identified as 34-year-old Aaron Alexis, a former Navy reservist and a current military contractor, the Washington FBI Field Office told CNN. His identity was confirmed by fingerprints and a picture ID card, the FBI said.
Authorities have not released a possible motive in the morning shooting at the headquarters for Naval Sea Systems Command that left 12 people -- and the gunman -- dead. But a friend said Alexis was locked in a dispute over money with the company that contracted him to work for the Navy.
Investigators also learned that Alexis had recently made contact with two Veterans Administration hospitals for apparent psychological issues, law enforcement sources told CNN on Tuesday.
Authorities said earlier that they are confident that Alexis was the lone gunman, bringing to an end a daylong police search for a possible second suspect.
Alexis was carrying a military-contractor ID that matched his appearance, a D.C. Metropolitan Police official told CNN on condition of anonymity.
Alexis used that ID to gain access to the Navy Yard, according to a U.S. law enforcement official with knowledge of the investigation.
He drove onto the installation and parked before walking a short distance to Building 197. Once inside, according to the official, Alexis made his way to an overlook above the atrium and opened fire into the cafeteria.
Initial reports said Alexis used an AR-15 semiautomatic rifle during the attack, but by Tuesday, law enforcement sources with knowledge of the investigation said that was not the case.
It is believed that Alexis had rented an AR-15, but returned it before Monday's shooting, the officials said. Investigators have recovered three weapons from the scene, including a shotgun that Alexis is believed to have brought into the compound. The other two weapons -- handguns -- the sources say, may have been taken from guards.
While the FBI was urging anyone with information about Alexis to come forward, investigators were focusing on reported incidents, including police run-ins, that portray a man with increasingly violent tendencies.
Alexis was believed to have arrived in the Washington area last week, when he reportedly checked into a hotel, according to someone who met him at the hotel. The person, who declined to be identified, said Alexis indicated that he planned to be in the area for several weeks.
At the time of the shooting, Alexis was working for The Experts, a subcontractor of HP Enterprise Services that was contracted to "refresh equipment used on the Navy Marine Corps Intranet network," according to a statement released by the company.
Alexis, who had Department of Defense security clearance, worked from September 2012 through January refreshing computer systems in Japan, said Thomas E. Hoshko, the CEO of The Experts.
His security clearance was renewed in July to carry out the same type of contract work at the Navy Yard, Hoshko said.
Alexis returned to work with The Experts that same month, he said. He worked at facilities in Rhode Island, North Carolina and Virginia for weeks at a time upgrading computer systems, Hoshko said.
No one reported having any problems with Alexis during those assignments, the chief executive said.
Alexis began working at the Navy Yard last week, though it was unclear whether he had actually begun working or was still securing his base clearance, Hoshko said.
There were no indications that Alexis had any ideological differences with the Navy or any disagreements with anyone at the Navy Yard, the U.S. law enforcement official said.
Alexis' family reeled at the news that he was believed to be the man behind the killings.
"What I do know is he wasn't that type of person," Anthony Little, who identified himself as Alexis' brother-in-law, told reporters outside his Brooklyn, New York, home. "I didn't really hear anything that would make me feel, as a newcomer to the family, that somebody should be watching him."
He said the family's initial reaction was "very distraught, very stressed out, tears."