Sept. 16, 2013 -- Aaron Alexis, the gunman who killed 12 people at the Navy Yard in Washington, D.C, before being shot and killed, is a former sailor who was detached from service in 2011, authorities said.
The FBI is now scrambling to learn anything and everything they can about the shooter's past. "No piece of information is too small," authorities said at a news conference today. Officials said they want to learn everything they can about Alexis' recent movement, contacts and associates.
But Alexis' previous brushes with the law offer glimpses of a man who may have had trouble managing his anger.
Alexis, 34, joined the Navy as a reservist in 2007 and got his rank in 2009. He was an aviation electrician and he was detached from service for a series of misconduct issues, a Navy official said.
He was born in Queens, N.Y., according to the FBI, and his last known residence was in Fort Worth, Texas. Alexis' father, mother and sister, who all live in Brooklyn, N.Y., were being questioned, law enforcement officials told ABC News.
Alexis worked for Hewlett-Packard as an IT subcontractor for the Navy, the company said. He was an employee of a company called "The Experts" that refreshed equipment used on the Navy Marine Corps Intranet network. It was unclear if he was working at the Navy Yard itself.
"We are deeply saddened by today's tragic events at the Washington Navy Yard," an HP spokesperson said in a statement. "HP is cooperating fully with law enforcement as requested."
The shooter's identity was confirmed based on partial fingerprint analysis. Authorities do not yet have a motive.
Alexis was previously arrested on May 6, 2004, in Seattle for shooting out the tires of another man's vehicle in what he later described as "an anger-fueled 'blackout,'" according to the Seattle Police Department.
He told cops he could not remember firing his gun at the man's car until an hour after the incident.
A Seattle detective spoke to Alexis' father, who was "curious" about the incident.
"Mr. Alexis then told me that his son had experienced anger management problems that the family believed was associated with PTSD," the detective wrote in a police report. "He confirmed that his son was an active participant in rescue attempts of September 11th, 2001."
Alexis was also arrested on Sept. 4, 2010, by Fort Worth police after he was accused of recklessly discharging a firearm inside the limits of a municipality, according to the Tarrant County District Attorney's Office.
"It was determined that Alexis was cleaning a gun in his apartment when it accidentally went off," the DA's office said in a statement. "A bullet entered an apartment upstairs. No one was injured."
After reviewing the case, the DA's office did not file a case.
Nutpisit Suthamtewakul, owner of Happy Bowl Thai in White Settlement, Texas, said was a "good and close friend" of Alexis. He said the two lived together for three or four years.
"I don't believe he did that," Suthamtewakul told ABC News. "He can be tough physically, but I don't think he'd kill people."
Suthamtewakul said Alexis liked to play games, drink and party. Alexis spoke Thai fluently, he said, traveled a lot for work and had been living in Washington for four or five months.
"He's not aggressive," he said. "He had a gun but that doesn't mean he's gonna shoot people. He had a concealed-weapons permit."
The FBI is asking that anyone with information on Alexis call 1-800-CALL-FBI.
Alexis' death brought the toll of the carnage at the Navy Sea Systems Command headquarters to 13, plus at least 12 wounded.
Additional reporting by ABC News' Pierre Thomas, Jim Scholz and Russell Goldman.