Before flying his single engine Piper PA-28 into the hulking black-glass office building Thursday morning, A. Joseph Stack III apparently posted a rambling screed on a Web site in which he railed against "big brother," the Catholic Church, the "unthinkable atrocities" committed by big business and the governments bailouts that followed.
In the note, signed "Joe Stack (1956-2010)" and dated Thursday, he said he slowly came to the conclusion that "violence not only is the answer, it is the only answer."
Law enforcement officials, speaking on condition of anonymity because the investigation was still going on, said the 53-year-old Stack apparently set fire to his house and posted the screed.
Stack's wife, Sheryl, planned to address the news media on Friday, the Red Cross said.
Some who knew Stack said he offered little hint of his anger before the attack.
"He didn't rant about anything," said Pam Parker, an Austin attorney whose husband played in a band with Stack. "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."
But in the self-described "rant," the author fumed about the IRS and wrote, "Nothing changes unless there is a body count."
"I have had all I can stand," he wrote, adding: "I choose not to keep looking over my shoulder at `big brother' while he strips my carcass."
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Stack took off from an airport in Georgetown, about 30 miles from Austin, and flew low over the Austin skyline before plowing into the side of the Echelon 1 office building just before 10 a.m. Flames shot from the building, windows exploded and terrified workers rushed to get out.
The Pentagon scrambled two F-16 fighter jets to patrol the skies over the burning building before it became clear it was the act of a lone pilot, and President Barack Obama was briefed.
"It felt like a bomb blew off," said Peggy Walker, an IRS revenue officer who was sitting at her desk. "The ceiling caved in and windows blew in. We got up and ran."
"I just thought it was unfair how an angry individual took out his anger on innocent people," Elva Liando, an IRS employee who works on the second floor, told CBS' "The Early Show" Friday.
"I didn't think it was an accident," she said.
Liando said she immediately fled the building upon the plane's impact and said people outside the office seemed in shock.
The outside of the second floor was gone on the side of the building where the plane hit. Support beams were bent inward. Venetian blinds dangled from blown-out windows, and large sections of the exterior were blackened with soot. It was not immediately clear if tax records were destroyed.
Crime scene tape surrounded the building Friday as Homeland Security, police and fire crews continued their investigation.
Emergency crews originally said people were missing inside the building, but later recovered two bodies. Austin Fire Department Battalion Chief Palmer Buck declined to discuss the identities of those found, but said authorities had now "accounted for everybody."
Thirteen people were injured - two critically - authorities said.
Austin Police Chief Art Acevedo said "heroic actions" by federal employees may explain why the death toll was so low.
Andrew Jacobson, an IRS revenue officer who was on the second floor when the plane hit with a "big whoomp" and then a second explosion, said about six people couldn't use the stairwell because of smoke and debris. He found a metal bar to break a window so the group could crawl out onto a concrete ledge, where they were rescued by firefighters. His bloody hands were bandaged.
The FBI launched an investigation and Rep. Michael McCaul, a Republican from Austin on the Homeland Security Committee, said the panel will take up the issue of how to better protect buildings from attacks with planes.
The tirade posted Thursday on a Web site registered in Stack's name began: "If you're reading this, you're no doubt asking yourself, 'Why did this have to happen?'"
He recounted his financial reverses, his difficulty finding work in Austin, and at least two clashes with the IRS, one of them after he filed no return because, he said, he had no income, the other after he failed to report his wife's income.
According to California state records, Stack had a troubled business history, twice starting software companies in California that ultimately were suspended by the state's tax board, one in 2000, the other in 2004. Also, his first wife filed for bankruptcy in 1999, listing a debt to the IRS of nearly $126,000.
Stack's father-in-law, Jack Cook, told The New York Times that he knew Stack had a "hang-up" with the IRS and his marriage had been strained. His wife had taken her daughter to a hotel to get away from Stack on Wednesday night, the newspaper said.
The blaze at Stack's home, a red-brick house on a tree-lined street in a middle-class neighborhood six miles from the crash site, caved in the roof and blew out the windows. Arson crews were at the home Friday investigating.
Elbert Hutchins, who lives one house away, said the house caught fire about 9:15 a.m. He said a woman and her daughter drove up to the house before firefighters arrived.
"They both were very, very distraught," said Hutchins, a retiree who said he didn't know the family well. "'That's our house!' they cried. 'That's our house!'"
Thursday was not the first time a tax protester went after an Austin IRS building. In 1995, Charles Ray Polk plotted to bomb the IRS Austin Service Center. He was released from prison in October of last year.
The tax protest movement has a long history in the U.S. and was a strong component of anti-government sentiments that surged during the 1990s. That wave culminated in the 1995 bombing of a federal building in Oklahoma City that killed 168 people. Several domestic extremists were later convicted in the plot.