Many of those who knew who knew Stack in Texas and California seem shocked that 53-year-old the software engineer would commit such an act, according to interviews with the Austin American Statesman and other outlets.
But some acquaintances and relatives quoted in the press were aware Stack had issues with the IRS. "I knew Joe had a hang-up with the I.R.S. on account of them breaking him, taking his savings away," his wife's stepfather told the New York Times.
A mechanic at an airport outside Sacramento where Stack kept his plane for four years starting in the late 90s remembers him as "cheerful" and "hardworking." He also recalled Stack talking about moving to Texas for tax reasons, the Modesto Bee reports.
Stack's beef with the IRS apparently went back 30 years, to the early 80s, when he seems to have been involved with a tax resistance movement that was percolating around the country, particularly in California. In the note he apparently wrote the day of the attack, Stack holds forth at length on his grievances with the IRS. (The note's authenticity has not been confirmed by authorities.)
He blames the IRS and other government agencies for hindering his business prospects, and for wrecking his retirement plans.
Not much about Stack's personal life is known, but it is clear he went through difficult periods.
He grew up at a Pennsylvania orphanage, and went to a couple years of community college in Harrisburg, according to the New York Times and the Statesman. During his college years, "I was living on peanut butter and bread (or Ritz crackers when I could afford to splurge) for months at a time," according to his note.
He later married a woman named Ginger and moved to California. They had a daughter. Stack and his wife divorced in 1999.
At the time, Ginger Stack filed for bankruptcy because she could not pay $125,860 in back taxes due for 1993 and 1998, the Los Angeles Times reports. Joe Stack had his own tax problems: two of his software businesses had their licenses suspended in California for failure to pay taxes or file returns.
Stack remarried in 2007 and was living with his wife and 12-year-old stepdaughter in a suburban neighborhood in North Austin.
"He was the perfect bandmate. I never saw him angry. I have no way to relate to him as an angry human being," band mate Ric Furley told the Los Angeles Times.
But in recent days, Stack's wife had become afraid of his "increasingly frightening anger," the New York Times reports, citing the wife's stepfather. She reportedly took her daughter to stay in a hotel on Wednesday.
The next morning, Stack allegedly set the family's house on fire before heading to the airport.