He told investigators he believed the man, a construction worker, was mocking him, but had no memory of shooting out the tires, the report said.
Investigators later spoke with Alexis' father, who told police that his son had anger management problems associated with post-traumatic stress disorder, which he suffered after working "as an active participant in rescue attempts" during the 9/11 attacks, the report said.
And in 2010, Alexis was arrested by Fort Worth, Texas, police but never charged over an allegation that he fired a gun through the ceiling of his apartment. According to records, he told police he accidentally fired it while cleaning it.
His last known address was outside of Fort Worth, where he was roommates for three years with Nutpisit Suthamtewakul, who described Alexis as his best friend.
Alexis befriended Suthamtewakul four years ago after he emigrated from Thailand.
Alexis taught him about American culture, Suthamtewakul told CNN. Alexis, he said, was fluent in Thai and attended a Buddhist temple.
When Suthamtewakul opened the Happy Bowl Thai Restaurant, Alexis would occasionally help out, waiting tables, he said.
The two were roommates until five months ago, when Suthamtewakul got married and Alexis had to move out.
Toward the end, Alexis spent a lot of time holed up in his room, keeping to himself, Suthamtewakul said.
On Monday, Suthamtewakul was stunned by the news that Alexis was said to be the shooter in the rampage at the Navy Yard.
"I can't believe he did this," he said. "He never showed any sign of violence."
But there were signs that Alexis was unhappy.
He was having a hard time trying to get on his feet, said Suthamtewakul's wife, Kristi. He helped out at the restaurant but not for pay.
"He was using this as an educational experience to help learn Thai," she said. He enjoyed making deliveries to homes, where the language was spoken. He talked about moving to Thailand.
But to Suthamtewakul, Alexis seemed "frustrated with life."
She is grieving. "He was like one of our best friends, like a brother to us and always willing to go out of his way to help us out with things," she said.
He was very frustrated with the company that contracted him to work for the Navy, according to another friend.
Alexis claimed he wasn't paid properly by the company after returning from a months-long assignment to Japan last year, said Michael Ritrovato, another former roommate.
It was unclear whether the dispute was over salary or expenses. Alexis just felt the company owed him money and had not paid him, Ritrovato said.
He is in shock over his friend's actions.
"He was an easygoing guy. I don't know of any reason for this," he said.
But Ritrovato knew Alexis was fascinated by guns. "He was ... knowledgeable with military rifles and handguns. At least he led us to believe he was. But nobody ever had the idea that he would use them in a derogatory way," he said.
Two days before the shooting, Alexis spent "a couple hours" shooting at Sharpshooters Small Arms Range in Northern Virginia before paying $419 for the Remington 870 shotgun -- after being approved by the federal background check -- and a small amount of ammunition, the store's attorney, J. Michael Slocum, said.