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 him 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.
Alexis served as a full-time Navy reservist between 2007 and 2011, according to military records. He achieved the rank of aviation electrician's mate 3rd class, working on aircraft electrical systems, the records show.
From February 2001 until February 2003, he worked for the Borough of Manhattan Community College as a college assistant in the administrative computing office, according to spokesman Barry Rosen.
Barry Williams, who was Alexis' supervisor there, said the suspect become easily frustrated over small things and could hold a grudge, but that he never saw him get violent.
Alexis, who managed switches and networking in the office, was a better than average worker, Williams said.
While the FBI are urging anyone with information about Alexis to come forward, investigators are focusing on reported incidents, including police run-ins, that portray a man with increasingly violent tendencies.
There were no indications that Alexis had any ideological differences with the Navy or any disagreements with anyone at the Navy Yard, according to a U.S. law enforcement official with knowledge of the investigation.
Alexis' family reeled at the news that he is 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 home in the Brooklyn borough of New York City. "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."
"You know, they didn't see it coming," said Little, who is married to Alexis' sister Naomi. "Their hearts are going out more to the victims and the people that got hurt because, you know, there's more lives lost and we don't need that right now. We really don't."
Melinda Downs, a friend of Alexis', said she spoke to him a week ago and he gave no indication of what was to come.
"It is like Dr. Jekyll and Mr. Hyde. Who was this guy?" she asked.
Downs described Alexis as intellectual.
"His mind was sound. He could hold conversations with the best of us," she said. "If he did (hear voices), he hid it very well."
She said Alexis had good relationship with his family, but a tough one with his father.
"You ask yourself, you go from denial, to reality, to fear, to blame. Is there something I could have done? ... Is there some type of behavior that I ignored or didn't see. That I could have prevented this. But there is no answers," Downs said.
Alexis appeared to have had sporadic run-ins with the law, dating back to at least 2004, when he was arrested in Seattle, accused of shooting out the tires of a man's truck in an anger-fueled "blackout," according to a Seattle Police Department report.