Story highlights Numerous incidents in Aaron Alexis' past show that he was troubled, prone to violence

Alexis shooting out the tires of car in Seattle in 2004 is the first in a string of instances

2010 brings another arrest after Alexis fires a bullet through the ceiling of an apartment

Last month, two years after his Navy discharge, he tells police he heard voices in three hotels

Navy Yard gunman Aaron Alexis left a trail of so-called red flags that, in hindsight, seem quite glaring, even if the impetus for this week's deadly rampage remains murky.

For almost 10 years, he showed that he was troubled -- and had a predilection for violence -- even if friends and family members familiar with his emotional problems seem floored that he was disturbed enough to shoot and kill 12 people in Washington on Monday.

They may seem like minor episodes when compared with Monday's shootings, but when pieced together, they provide ample fodder for critics who question how Alexis maintained the security clearance that gave him access to the Navy Yard.

2004 'blackout'

On the morning of May 6, 2004, Alexis fired his Glock into two tires of a Honda Accord near a Seattle home where he was staying. He was arrested and charged with malicious mischief.

Alexis told police the car's owner, a construction worker, had disrespected him, leading to an anger-fueled "blackout," according to a police report.

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His father told Seattle police that Alexis had post-traumatic stress disorder after working as "an active participant in rescue attempts" after the 9/11 attacks, the report said. Alexis' dad further told police his son had anger management issues related to PTSD.

"It appears as if investigators were aware of the incident, interviewed him and were satisfied that it did not preclude granting the clearance," a senior naval officer said of Alexis' 2007 enlistment.

2008 nightclub arrest

About five months after being granted a "secret" security clearance -- the year after joining the Navy -- Alexis was kicked out of a metro Atlanta club for damaging the furnishings, according to a police report.

Outside, Alexis cursed profusely, and when he defied police orders to stop, they arrested him for disorderly conduct, the report said.

The arrest was integral in the Navy's decision to try to end his military career, which wouldn't culminate for another three years, but Alexis was never stripped of his security clearance.

2010 gunfire incident

Fort Worth, Texas, police arrested Alexis in September 2010 after he allegedly fired a bullet through his ceiling into a neighbor's apartment.

According to records, he told police he accidentally fired the weapon while cleaning it. He was calm when police arrived . He was never charged.

Texas was Alexis' last official address, and friend Kristi Suthamtewakul said he spoke Thai, practiced meditation at a Buddhist temple and participated in his community. But he also hinted at a residual anger

"One of the things he talked about was 9/11 and how he was there and he saw the towers come down from where he was working," Suthamtewakul said. "He had an anger towards the terrorists who did that and took innocent people."

2011 Navy discharge

When the Navy began pursuing Alexis' general discharge, a dismissal that could have affected his security clearance, he had eight instances of misconduct on his record. Among them were insubordination, disorderly conduct, drunkenness and unauthorized absences from work, a U.S. defense official said.

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He eventually left the service with a less-severe honorable discharge because there were no convictions or evidence to necessitate a general discharge, the official said.

Alexis was allowed to keep his security clearance so long as he used it in another official capacity within two years, which he did after gaining employment in September 2012 with a contractor, refreshing computer systems in Japan.

In recent weeks, he sought help from a Veterans Affairs hospital in Rhode Island, his second such visit to a VA facility. While authorities are investigating the circumstances of those visits, sources differ on why Alexis wanted help, variously saying he was either hearing voices or having trouble sleeping

Suthamtewakul recalled Alexis expressing impatience with the VA: "He was very frustrated with the government and how as a veteran he didn't feel like he was getting treated right or fairly."

August 'microwave machine' allegation

Last month, police in Newport, Rhode Island, responded to a harassment complaint at a Marriott hotel. There, Alexis told them that someone "had sent three people to follow him and to talk, keep him awake and send vibrations into his body," a police report said.

These individuals had followed him to three hotels in the area, Alexis told police, and spoke to him through the walls and floor and used "some sort of microwave machine" that sent "vibrations through the ceiling, penetrating his body so he cannot fall asleep," according to the August 7 report

Alexis also told authorities, according to the report, that "he does not have a history of mental illness in his family and that he never had any sort of mental episode." Police notified Navy officials, the report said.

Asked for comment, Naval Station Newport officials referred CNN to the FBI, which had no comment.