In a Web diary written before the crash, Joseph Stack , outraged at loopholes that benefit large corporations but not average Americans.
But Stack, who used to play in the Billy Eli Band, was described as "easy going" by the band's manager.
"He talked politics like everyone but didn't show any obsession," said Pam Parker, the wife of Billy Eli and manager of the band. "The letter sounded like his voice but it was nothing I ever heard him say."
Parker told CBS News that Stack had a full-time job and had just gotten married when he stopped playing with the band a year and a half ago.
Parker said that she saw Stack six weeks ago and he was "his usual easy going" self.
Facebook Groups Support Domestic Terrorist
Father-in-Law: Pilot Had Hang-Up Over IRS
Austin Plane Attacker's Wife to Speak
IRS Worker: Austin Attack "Unfair"
Austin Pilot Left Anti-IRS Suicide Note
"Clearly there was crazy in him but it must have been way in the back of his head, it wasn't who Joe was," she added.
Patrick Beach, a writer for the Austin American Statesman who practiced in a band with Stack and his wife Cheryl, says he's shocked.
"It seems extremely out of character," he told CBS News correspondent Don Teague. "He was the quintessential, stereotypical, straight-out-of-central-casting, mild-mannered, bespectacled engineer type."
According to California Secretary of State records, Stack had a troubled business history, twice starting software companies in California that ultimately were suspended by the state's Franchise Tax Board.
In 1985, he incorporated Prowess Engineering Inc. in Corona. It was suspended two years later. He started Software Systems Service Corp. in Lincoln in 1995 and that entity was suspended in 2001. Stack listed himself as chief executive officer of both companies.