The picture emerging of the Aaron Alexis, the dead gunman in Monday's Navy Yard shooting, is a study in contrasts -- one of a man who practiced languages and meditated, and another of a cold-blooded killer.
Alexis, who was from New York City, served as a full-time Navy reservist between 2007 and 2011, but was honorably discharged after a "pattern of misconduct," a U.S. defense official with knowledge of the investigation told CNN on condition of anonymity.
According to police reports, he was involved in shooting incidents in Seattle and Fort Worth, Texas.
In Seattle, he was arrested in 2004 for shooting out the tires of another man's car in what Alexis told police was an anger-fueled "blackout."
In Fort Worth, a neighbor in his apartment complex called police after he fired a gunshot into his floor and through her ceiling in 2010. No charges were filed, but the woman told police she was "terrified" of Alexis and believed the shooting was intentional because he had confronted her for being too loud.
While no motive for the shooting has been revealed, a friend told CNN Alexis was locked in a dispute over money with the company that contracted him to work for the Navy.
Acquaintances told ABC News he had been stewing over a perceived slight for about a year, and kept asking friends for financial help.
But while one friend in Texas admitted Alexis was "frustrated with life," he never showed signs of violence, Nutpisit Suthamtewakul told CNN.
A practicing Buddhist who spoke Thai fluently, he was described by friends as quiet and introspective.
Alexis' family, meanwhile, reeled at the news that he was believed to be behind the killings. "You know, they didn't see it coming," said Anthony Little, who is married to Alexis' sister Naomi. "Their hearts are going out more to the victims and the people that got hurt because, you know, there's more lives lost and we don't need that right now. We really don't."
Investigators say Alexis had recently made contact with two Veterans Administration hospitals for apparent psychological issues.
He was also fascinated by guns, and woulud stay up all night playing military-style video games, friends said.
20 individuals have been arrested in connection with a five-month long investigation that involved the Santa Barbara Police Department, and the Bureau of Alcohol, Tobacco, Firearms and Explosives, into the sales of illegal narcotics and firearms.