Alexis, who served in the Navy between 2007 and 2011, was described by friends as a Buddhist and Thai speaker, NBC News reported.
One friend told NBC that Alexis "could not be the shooter." Alexis died along with a dozen others on Monday.
After being discharged from the Navy, Alexis got a job with a company called The Experts, a subcontractor to Hewlett Packard on a Navy Marine Corps Intranet network contract, according to the Washington Post.
Through that job, Alexis apparently had the security clearance that enabled him to get onto the Navy Yard, the Washington Post reported.
Police believe Alexis had a concealed carry permit for a weapon despite two prior incidents related to guns, the Associated Press reports. Alexis was apparently arrested in 2010 for discharge of a firearm in Forth Worth, where he lived until recently, according to The Washington Post.
In 2010, Alexis' gun apparently went off while he was in his apartment. The bullet shot a hole through his upstairs neighbor's floor.
NBC News in Dallas/Forth Worth obtained the arrest report from the 2010 incident. An excerpt from the narrative is posted below:
[The upstairs neighbor] also told me that her downstairs neighbor ARR (Alexis,Aaron) has called the police several times on her for being loud however the police always said they didn't hear anything and no action was taken. She said that several days ago Aaron confronted her in the parking lot about making too much noise. June told me that she is terrified of Aaron and feels that this was done intentionally.
Alexis reportedly told police that he was cleaning his gun when it accidentally went off.
Alexis was also arrested in Seattle in 2004 for shooting out the tires on a man's vehicle, according to the city's crime blotter. He reportedly told police the incident was brought on by an anger-fueled "blackout."
He also told police that he was " present during the tragic events of September 11, 2001" and that the events disturbed him and left him with Post Traumatic Stress Disorder. Alexis is originally from New York City. His father told police that he participated in the rescue attempts after the 9/11 attacks.
Alexis was getting his bachelor's degree in aeronautics at Embry-Riddle Aeronautical University, USA Today reported. Friends told USA today that he was an easygoing guy but complained about having trouble finding work. He carried a pistol in his belt, friends said.
The Monday morning shooting at Navy Yard left 13 dead and several others wounded. Alexis is reportedly among the dead, according to NBC. The New York Daily News reports that he was killed in a gun battle with police.
The Guardian's U.S. National Security editor says Alexis once served in the Navy:
Navy's Rear Adm. John Kirby confirms Aaron Alexis was the shooting suspect. A Navy aviation electrician's mate; served 5/07-1/11.
— Spencer Ackerman (@attackerman) September 16, 2013
Alexis also reportedly received the National Defense Service Medal and the Global War On Terrorism Service Medal, according to The Guardian. The Global War On Terrorism medal is awarded to every member of the U.S. Armed Forces serving at least 30 consecutive days supporting operations of the Global War On Terror.
CNN reporters are citing a U.S. defense official saying Alexis was dishonorably discharged from service after a "pattern of misconduct."
Police were initially seeking two other suspects in the case. One of the men they were seeking has been cleared. Law enforcement officials have not identified a motive for the shooting.
UPDATE: The FBI is now seeking information on Alexis:
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