WASHINGTON — Aaron Alexis lived for a time in a bungalow in the woods near a Buddhist temple in Fort Worth, Texas, where he occasionally joined Thai immigrants in meditation. Aaron Alexis died Monday in a gun battle with police in a building at the Washington Navy Yard after he killed at least 12 people.

In between, the man named as the shooter in Monday’s mass murder at Navy Yard Building 197 was discharged from the Navy Reserve, arrested for shooting a bullet into his downstairs neighbor’s apartment and then asked to leave his Fort Worth apartment.

A Navy official, speaking on condition of anonymity, said Alexis was discharged in January 2011 for “a pattern of misconduct” and that the 2010 gun incident in Texas played a role in his departure.

Another Navy official said Alexis was given a “general discharge,” a classification often used to designate a blemished record of performance. In some cases, a general discharge can make it difficult to land a civilian job.

Alexis, 34, arrived in Washington about four months ago, friends said. He had worked recently for a defense contractor called The Experts, which is a subcontractor on an HP Enterprise Services contract to work on the Navy Marine Corps’s Intranet network, according to Hewlett-Packard spokesman Michael Thacker. Officials at The Experts did not immediately reply to phone messages. It was unclear if Alexis was still employed by that subcontractor, or if his work had brought him to the Navy yard.

Investigators Monday night were examining how Alexis got into the Navy yard, and whether he had or used the identification card of a former Navy petty officer that was found near Alexis’s body after police killed him.

Those who knew Alexis in recent years describe him as a “sweet and intelligent guy” (a regular customer at the Thai restaurant where he worked as a waiter), as “a good boy” (his landlord), but also as someone who was “very aggressive,” someone who seemed like he might one day kill himself (a lay worker at the Buddhist temple where Alexis worshipped.)

In 2004, Alexis was arrested in Seattle after he fired three shots from a Glock pistol into the tires of a Honda Accord that two construction workers had parked in a driveway adjacent to Alexis’ s house. Alexis’s father told Seattle detectives then that his son “had experienced anger management problems that the family believed was associated with PTSD,” or post-traumatic stress disorder, according to the police report. The father said that Alexis “was an active participant in rescue attempts of Sept. 11, 2001.”

Alexis’s own explanation for his behavior that day: the construction workers had “mocked” and “disrespected” him and then he had had “a black-out fueled by anger.”

Alexis was not charged in the Seattle incident.

More recently, Alexis struck those who crossed his path as a man of sharp contrasts. He studied the Thai language, visited Thailand for a month, was studying for an online degree in aeronautical engineering and seemed to enjoy conversing with customers, according to friends, customers and fellow worshippers. But some of those same people said that Alexis had an aggressive streak, one that caused them to keep their distance and avoid personal questions.

Alexis grew up in Brooklyn, N.Y., with his mother Sarah and father Anthony Alexis, according to his aunt Helen Weeks. “We haven’t seen him for years,” Weeks said in a phone interview. “I know he was in the military. He served abroad. I think he was doing some kind of computer work.”

Alexis spent nearly four years in the Navy as a full-time reservist from May 2007 until he was discharged in January 2011, according to a summary of personnel records released by the Navy. A Navy official, speaking on condition of anonymity, said Alexis was discharged from the service in January 2011 for “misconduct,” and that the 2010 firearms incident in Texas played a role in his departure.

He achieved his final rank of Aviation Electrician’s Mate 3rd Class in December 2009.

Navy Secretary Ray Mabus said Alexis worked as a defense contractor after his discharge. A deleted LinkedIn page under Alexis’s name listed SinglePoint Technologies, a Richmond, Va., firm, as his employer; the company did not return a call seeking comment.

Alexis spent the bulk of his service time – from 2008 to 2011 – assigned to the Fleet Logistics Support Squadron 46 at Naval Air Station Fort Worth in Texas, from 2008 until he left the service in 2011, records show. He was awarded the Global War on Terrorism Service Medal and the National Defense Service Medal – two awards of minor distinction.

In Fort Worth, Alexis lived for a time in a gated townhouse community called Orion at Oak Hill. In September, 2010, police were called to Apartment 2023 after Alexis’s downstairs neighbor complained that Alexis had fired a bullet through his floor and into her ceiling below.

The woman told police that she had had occasion to call them about Alexis several times for being too loud, but that nothing had been done. The woman said Alexis had confronted her a few days earlier in the complex’s parking lot, where he complained that she had been making too much noise. The woman told police that “she is terrified of Aaron and feels that this was done intentionally,” the police report said.

Police made three attempts to contact Alexis by knocking on his door, but he didn’t respond. Only after police called in firefighters to force entry into his apartment did Alexis emerge. Alexis then told police that he had been cleaning his gun while he was cooking and his hands had become greasy and the weapon discharged by accident, according to the police report.

“He told me that he began to take the gun apart when his hands slipped and pulled the trigger, discharging a round into the ceiling,” the officer wrote.

Alexis was arrested for improper discharge of a firearm, but a spokesman for the county district attorney’s office said no charges were brought in the matter. Alexis’s mugshot from that arrest shows a clean-shaven man with soft eyes and an impassive expression.

A couple of weeks later, the apartment complex began eviction proceedings against Alexis, according to county court records.

Soon after that, Srisan Somsak, a Thai immigrant in Fort Worth, met Alexis at the Wat Busayadhammavanaram Meditation Center, where Alexis had occasionally shown up for meditation starting in summer of 2010. Alexis said he needed a place to stay and Somsak offered to rent him the two-bedroom white bungalow behind the center – if he promised not to smoke or drink.

Alexis rented the place for $600 a month, lived up to those promises and never missed a payment, said Somsak, 57.

“He’s a good boy,” said Somsak, who spoke English with a heavy accent. “Everybody would say, ‘He’s a good boy’ here. Not only me. He’s a good boy.”

Alexis occasionally meditated at the temple and helped out there when needed, said Somsak, who was pleased to find that his tenant studied the Thai language and visited Thailand.

On Monday, as word spread about the shooting, the temple filled with members eager to share their recollections of Alexis. “They don’t believed it that he could kill 12 people like that,” Somsak said. “I think probably somebody tried to put him down. I don’t know. “Did somebody try to discriminate against him? That’s the only way. That’s what I keep thinking.”

Somsak asked Alexis only once about why he had left his job at the naval base. It was a brief conversation.

“I asked him, ‘Why you quit the job with the government?” Somsak said. “He said, ‘Somebody doesn’t like me.'”

Somsak left it there because “I don’t want to go too deep with him.”

Alexis visited the center about twice a week and was known as a quiet, if tightly wound, participant, according to a temple staff member.

“He would help people if they came in carrying heavy things,” said J. Sirun, an assistant to the monks. “From the outside, he was a quiet person. But on the inside, I think he was very aggressive. He did not like to be close with anybody, like a soldier who has been at war.”

Sirun said he avoided Alexis, who preferred to keep to himself. But Alexis was no longer; he had many Thai friends and spoke Thai “very well,” Sirun said. “He understood about 75 percent of the language.”

During that period, Alexis worked as a waiter and delivery man for the Happy Bowl Thai restaurant in White Settlement, Texas, according to customers and workers there. Customers saw him studying Thai at a table there during his off hours.

Alexis stopped showing up at the Buddhist center early in 2011, Sirun said.

“I didn’t think he could be this violent,” Sirun said. “I would not have been surprised to hear he had committed suicide. But I didn’t think he could commit murder.”

Relatives contacted by reporters were stunned to hear that he was involved in the Washington shootings. “I’d be shocked if it was him, but I don’t know,” said Weeks, his aunt, her voice trailing off.

Even as he worked for the defense contractor, Alexis was pursuing a bachelor’s degree in aeronautics as an online student at Embry-Riddle Aeronautical University. The university, in Daytona Beach, Fla., said Alexis enrolled in July 2012, via the school’s Fort Worth campus. He remained a student in good standing, said Melanie Hanns, Director of University Communications.

“He was enrolled for this semester,” she said.

FBI Assistant Director Valerie Parlave asked the public to call 1-800-CALL-FBI with details about Alexis: “No piece of information is too small.”

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