Alexis joined the Navy as a reservist from 2007 to 2011 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. The suspect had a security clearance that allowed him onto the Navy Yard as part of his civilian subcontracting work, officials said.
Alexis was arrested 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.
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 Sept. 11, 2001."
Suthamtewakul said 9/11 had a profound impact on Alexis' life because he was living in New York City at the time of the attacks on the World Trade Center.
"He was living in New York, being from New York and he talked about how angry he was with the terrorists who would take innocent lives," she said.
Melinda Downs said she has known Alexis for about a year and despite always having a smile on his face he spoke about depression.
"You never saw him without a smile on his face or saying something to make a person laugh and when you would see him looking down I would just ask, 'Aaron, are you okay?' and he would be like, 'I'm okay. I'm okay.' And I would just keep talking to him until he would lighten up," Downs told Good Morning America today.
Downs spoke to Alexis as recently as last week and said he was in Washington D.C.
"He called checking in as usual," she said. "He was just his old chipper self."
ABC News' Pierre Thomas, Christina Ng and Luis Martinez contributed to this report.