Signs that Aaron Alexis had a violent streak surfaced at least as far back as 2004, when he removed a gun from his waistband, chambered a round and shot out a man's car tires in a burst of anger triggered by what he said was "disrespect."
What drove 34-year-old Alexis, the man the FBI believes was responsible for the murders, to enter the Washington Navy Yard and open fire from a fourth-floor balcony overlooking a busy cafeteria in a spree that left 13 people dead, including himself, is now the subject of intense scrutiny by law enforcement.
Despite worshipping at a Buddhist temple and earning two awards for service during his four years in the U.S. Navy Reserves, flashes of violence have long pointed to Alexis' dangerous side, his record shows.
Alexis, a black man born in New York City's borough of Queens, was discharged from the military in 2011 after a series of what a Navy official described as "misconduct issues."
His police record shows the six-foot-one-inch, 190-pound Alexis was arrested over the tire shooting incident in Seattle in 2004, and once again on gun-related charges in Texas in 2010, for shooting through his noisy upstairs' neighbor's floor.
His father, Algernon Alexis, said he believed his son suffered from post-traumatic stress disorder, triggered by his involvement in rescue efforts during the tragic events of September 11, 2001. Seattle police said in a report the son told them he was deeply disturbed by the experience.
In a 2004 report, the Seattle police said: "He perceived (a construction worker) had disrespected him and how that perception lead to what Alexis described as a 'black-out' fueled by anger. He said that he didn't remember pulling the trigger of his firearm until about one hour later."
Neither New York City officials nor a group representing first responders in New York was immediately able to confirm that Alexis was involved in the September 11 rescue efforts.
Years later, in 2010, Alexis was arrested in Fort Worth, Texas, for discharging his weapon, shooting through his apartment ceiling into the upstairs apartment of a neighbor who told police she was "terrified" of him after he complained she made too much noise, according to a police report.
Authorities did not press the case after determining the gun accidentally fired while Alexis was cleaning it. The housing complex, Orion at Oak Hill apartments, evicted him.
Public records indicate that since 1998, Alexis has lived in New York and Washington state, where he was sued for debts, as well as Texas.
His full-time military service started when he enlisted in the U.S. Navy's Reserve in May 2007, rising to the rank of Aviation Electrician's Mate 3rd Class, and receiving the National Defense Service Medal and the Global War on Terrorism Service Medal before returning to civilian life in January 2011, a Navy official told Reuters.
At some point he was a civilian contractor for the U.S. Navy in the information technology area. At the time of the shooting, Alexis was employed by a company called The Experts, a subcontractor for Hewlett-Packard that serviced computer equipment, the company said.
In the role, Alexis had "secret" clearance and was assigned to start working there as a civilian contractor with a military-issued ID card, said Thomas Hoshko, chief executive of The Experts. Alexis had also worked for the firm in Japan in 2012, he said.
His father said he was currently "in school and working at a job" at a private company where he held a "computer-related" position outside of New York.
In the past, Alexis worked at the "Happy Bowl" Thai restaurant in White Settlement, Texas, where he often complained about money problems, according to the owner's wife.
Kristi Suthamtewakul, 35, described Alexis as a friendly man and a great conversationalist, but said he was "upset with the government about his benefits" and could not afford to pay his utility bills or fix his car.
She also said he carried a gun tucked into the side of his pants every time he worked at the restaurant.
"You wouldn't even know it because his shirt was down," she said.
In New York, his brother-in-law, Anthony Little, said it had been several years since Alexis spoke with his family in Brooklyn.
"He is not as close as the normal person with his family," Little said.
(Additional reporting by Phil Stewart, Karen Brooks, Marice Richter, Susan Cornwell, Mark Hosenball, Victoria Cavaliere, Jonathan Allen, Edith Honan and Lisa Maria Garza; writing by Barbara Goldberg; editing by Grant McCool and Jackie Frank)