AUSTIN – Why Andrew Joseph Stack III flew his plane into an office building isn't a mystery.

"I am finally ready to stop this insanity. Well, Mr. Big Brother IRS man, let's try something different; take my pound of flesh and sleep well," he wrote.

That's the end of a lengthy missive that Stack, a computer software engineer, finished at 1:42 a.m. Thursday and posted on a company Web site.

Hours later, he set fire to his red brick home in Austin. He then drove to Georgetown Municipal Airport, climbed into his single-engine plane and took off about 9:44 a.m. He had no flight plan but did have a target: a four-story office building in northwest Austin that houses about 190 Internal Revenue Service workers, many of them civil and criminal investigators.

He slammed his plane into the building – the last, desperate move by a man overwhelmed by personal and business failures, trying to strike out at enemies all around him.

"Nothing changes unless there is a body count," he wrote.

Although his online letter – part manifesto and part rant – left myriad questions, Stack focused his rage on the U.S. tax system, accusing the IRS of damaging his career.

"Why did this have to happen?" Stack wrote. "The simple truth is that it is complicated and has been coming for a long time."

He apparently began writing it several months ago, "intended to be therapy in the face of the looming realization that there isn't enough therapy in the world that can fix what is really broken."

Joseph Stack

As a child, Stack wrote, he and others were schooled to possibly give up their lives to preserve the principles of the nation's founders.

"One of these was 'no taxation without representation.'... [and] these days anyone who stands up for that" is "labeled a 'crackpot,' traitor, and worse," Stack wrote.

Stack apparently grew up in an orphanage in Pennsylvania, and at age 18 or 19, he learned about the "significance of independent" while living alone as a student in Harrisburg, Pa. That's where, he said, an elderly neighbor lived on Social Security because her husband, a steel worker, had lost his retirement in the collapse of his employer.

"I decided that I didn't trust big business to take care of me, and that I would take responsibility for my own future and myself," he wrote.

But he had a troubled business history, starting two software companies that California tax regulators suspended.

Stack moved to California in the 1980s, when he and others took part in "tax code readings and discussions" about tax exemptions that he said make "institutions like the vulgar, corrupt Catholic Church so incredibly wealthy."

"We carefully studied the law [with the help of some of the 'best,' high-paid experienced tax lawyers in the business] and then began to do exactly what the 'big boys' were doing," he wrote.

Without providing details, he said: "That little lesson in patriotism cost me $40,000+ 10 years of my life, and set my retirement plans back to 0. It made me realize for the first time that I live in a country with an idealogy [sic] that is based on a total and complete lie."

Stack said the 1986 federal tax law change damaged his career by how it treated workers – such as contract engineers – for tax purposes. That's an apparent reference to a ruling that contractors are not employees and entitled to certain benefits.

He divorced his first wife, Ginger Stack, of Hemet, Calif., in 1999, and she has had little contact with him since, said her husband.

After the divorce, Stack said, he began to "finally pick up some speed," but he blamed the dot-com bust and the 2001 terrorist attacks that disrupted travel for crippling his business.

"Our leaders decided that all aircraft were grounded for what seemed like an eternity; and long after that, 'special' facilities like San Francisco were on security alert for months. This made access to my customers prohibitively expensive," he said.

Stack said he moved to Austin in 2004 but "never experienced such a hard time finding work."

"To survive, I was forced to cannibalize my savings and retirement, the last of which was a small IRA. ... I filed no return that year thinking that because I didn't have any income there was no need. The sleazy government decided that they disagreed," he wrote.

Travis County records show that Stack married music teacher Sheryl Housh Mann in July 2007. Two months earlier, he bought a house on Dapplegrey Lane in Austin, taking out a deed of trust for $188,000.

He played bass guitar with the Billy Eli band in Austin.

Band mates say they never saw the angry side of Stack. They recalled a quiet father who traveled to Norway every year to visit his daughter and grandchildren. They never heard Stack talk about politics, about taxes, about the government – the sources of pain that Stack claims drove him to his death.

"I read the letter that he wrote. It sounded like his voice, but the things he said I had never heard him say," said Pam Parker, an Austin attorney whose husband was one of Stack's band mates. "He didn't rant about anything. He wasn't obsessed with the government or any of that. ... Not a loner, not off in a corner. He had friends and conversation and ordinary stuff."

Michael Cerza, who played drums, piano and trumpet with Stack, said, "I don't know what to base his madness on. It must have been lurking beneath the surface."

Many neighbors in the middle-class North Austin neighborhood where the Stacks lived for more than two years said they had little contact with them.

"I never saw him," said Elbert Hutchins, who lives two doors down. "I used to see her coming and going, but I wouldn't recognize him."

Hutchins, who is retired, was working at his computer Thursday morning when he and his wife heard a loud noise and rushed out to investigate. They saw flames and smoke billowing out of the second-story windows of the Stack home and called 911.

Hutchins later saw Sheryl Stack and her daughter drive up to the house before firetrucks arrived.

"They both were very, very distraught," he said, adding that Sheryl Stack cried, "That's our house!" The woman and her daughter later went to another neighbor's home and remained inside, declining to talk to reporters.

With them were FBI agents and the Texas Rangers, as well as Austin police investigators and representatives of the American Red Cross.

Natalie Kunkel, who lives near the Stacks, said she had no contact with Stack but used to talk to Sheryl Stack two years ago when their daughters swam together at a neighborhood pool.

She described Sheryl Stack and her 12-year-old daughter as "very friendly" until about a year ago.

"I honestly don't know what their lives have been like lately," she said.

Staff writers Christy Hoppe, Steve McGonigle, The Associated Press and the Riverside Press-Enterprise contributed to this report.