Washington Navy Base Killer: An Armed Buddhist

Aaron Alexis, who the FBI said carried out a deadly rampage at the Washington Navy Yard, lived a life of dramatic contrasts.

The 34-year-old was a former Navy reservist, a defence subcontractor for IT giant Hewlett-Packard and a convert to Buddhism who was taking an online course in aeronautics.

But Alexis, who grew up in Brooklyn, New York, also had flashes of temper that led to run-ins with police over shootings in Fort Worth, Texas, and Seattle.

While some neighbours said he was "nice", others said they were afraid of him.

But authorities are still trying to establish what motivated Alexis to carry out the shooting, killing 12 people before being gunned down by police himself.

It has been reported that Alexis was suffering from mental health issues at the time of the shooting and had been hearing voices.

When Alexis was arrested over a shooting incident in Seattle in 2004, he told police he was present during "the tragic events of September 11, 2001" and described "how those events had disturbed him".

At the time, his father also said his son had anger management problems related to post-traumatic stress brought on by the terrorist attacks.

Seattle police said Alexis was arrested and charged for shooting out the tyres of a vehicle in what he later described to detectives as an anger-fuelled "blackout".

Two construction workers had parked their car in the driveway of their work site, next to a home where Alexis was staying, the police report said.

When detectives interviewed workers at the construction site, they told police Alexis had stared at construction workers at the job site daily for several weeks prior to the shooting.

The owner of the construction business told police he believed Alexis was angry over the parking situation around the site.

According to the police account, Alexis had also told detectives he thought he had been "mocked" by construction workers on the morning of the incident.

Then in May 2007, Alexis enlisted in the Navy reserve. He was discharged for misconduct in early 2011.

"There is definitely a pattern of misconduct during his service," a US military officer, who spoke on condition of anonymity, told news agency AFP.

But Alexis did receive the National Defence Service Medal and the Global War on Terrorism Service Medal.

Both medals are issued to large numbers of service members who have served since the 9/11 attacks.

It was while he was still in the reserves that a neighbour in Fort Worth reported she had been nearly struck by a bullet shot from his downstairs apartment.

The neighbour told police she was scared of Alexis and felt he fired intentionally because he had complained about her making too much noise.

Fort Worth police arrested Alexis about the neighbour's report.

Alexis admitted to firing his weapon but said he was cleaning his gun when it accidentally discharged. He was released without charge.

After leaving the reserves, Alexis was a popular waiter and delivery driver at the Happy Bowl Thai restaurant in Fort Worth.

He visited Thailand and learned some of the local language so could speak to Thai customers in their native tongue.

"He was a very nice person. It kind of blows my mind away. I wouldn't think anything bad at all," former co-worker Afton Bradley said.

Other friends say Alexis was contemplating moving to Asia.

A former acquaintance, Oui Suthametewakul, said Alexis lived with him and his wife from August 2012 to May 2013 in Fort Worth.

He said they parted ways because Alexis was not paying his bills.

Despite this, Mr Suthametewakul described Alexis as a "nice guy" - but he sometimes carried a gun and would frequently complain about being the victim of discrimination.

Mr Thairintr said Alexis told him he was upset with the Navy because "he thought he never got a promotion because of the colour of his skin. He hated his commander".

Mr Thairintr said Alexis was "very devoted Buddhist" who prayed at a local temple.

"We are all shocked. We are non-violent. Aaron was a very good practitioner of Buddhism. He could chant better than even some of the Thai congregants," said Ty Thairintr, who last saw Alexis five weeks ago.

"There was no tell-tale sign of this behaviour."

In the early 2000s, before he moved to Seattle, Alexis lived with his mother in New York City, said Gene Demby, who said he dated one of Alexis' younger sisters at the time.

"He was insecure. He was like a barbershop conspiracy theorist, the kind of guy who believes he's smarter than everyone else," said Mr Demby, the lead writer for National Public Radio's Code Switch blog about race and culture.

"He also was kind of like perpetually aggrieved, but not megalomaniacal or delusional."