A Texas pilot flew a small plane into an Austin office complex today and authorities are investigating links to a hate-filled note found on the Internet, telling the IRS to "take my pound of flesh and sleep well."
Investigators are trying to determine whether Andrew Joseph Stack, the man identified by authorities as the pilot of the plane, is the same person as "Joe Stack," the name signed to the online rant that warns, "Desperate times call for desperate measures."
The office building complex where the plane crashed houses IRS offices employing about 190 people. The Austin Fire Department has concluded its search of the building and located the remains of two victims who have not yet officially been identified.
Police earlier said Stack died in the crash and two other people were taken to the hospital -- though later it was not clear whether or not those were the two people whose remains were found.
One of the injured was taken to the Brook Army Medical Center's burn unit. Referring to the missing person, Austin Police Chief Art Acevedo said, "The prospects are not very positive for this person at this time."
Watch "World News with Diane Sawyer" tonight at 6:30 ET for more on the pilot's suicide mission .
The online note appears to have a taken responsibility for the attack on the IRS in an anger-fueled rant that was posted online and was signed signed "Joe Stack (1956-2010)".
Federal officials investigating the note believe it have been written by Stack and consider it evidence, a sort of manifesto to help understand motive. The web page has been taken down at the request of federal authorities.
The note was titled "Well Mr. Big Brother IRS Man … take my pound of flesh and sleep well." It details years spent working and paying taxes, but not reaping the benefits of what he considered to be a functional government.
"I choose to not keep looking over my shoulder at 'big brother' while he strips my carcass, I choose not to ignore what is going on all around me, I choose not to pretend that business as usual won't continue; I have just had enough," the note reads.
"I can only hope that the numbers quickly get too big to be white washed and ignored that the American zombies wake up and revolt; it will take nothing less," he wrote.
While firefighters battled the huge blaze at the office complex, other firefighters were working to contain a fire at Stack's house, which he apparently touched off before heading for his plane.
The Federal Aviation Administration confirmed today that the plane, a Piper Cherokee, took off from Georgetown Municipal Airport around 9:40 a.m. The FAA said the pilot did not file a flight plan or communicate with air traffic controllers once in the air.
President Obama Notified of Austin Plane Crash
Department of Homeland Security officials were quick to say they did not believe the crash was an act of terrorism, but White House officials said both President Obama and Homeland Security Secretary Janet Napolitano were notified about the crash, and Norad launched two jet fighters to patrol over Austin as a precaution.
Eyewitnesses who saw the plane slam into the building said the pilot appeared to be in control of the plane in the moments before the crash.
"It hit it and the strange thing was the engine seemed to me to running at full power. It didn't seem like the plane was in trouble. It was going full blast. It's not a very fast airplane, but this thing was really moving fast," pilot Jerry Cullen told ABC's Austin affiliate KVUE.
Beth Jones told ABCNews.com that she was headed downtown on Highway 183 when she spotted the plane overhead and immediately noticed how low it was flying.
"The plane was just coming down," she said. "He was so low you could actually see him in the plane." She said the plane flew "just straight, right in" to the complex.
Dawn Clopton, Austin Fire Department division chief, said the impact engulfed several floors of the building in flames.
In the apparent suicide note, the author rages against everyone from President George W. Bush to deceased New York Senator Patrick Moynihan. Near the end, he takes aim at Austin accountant William Ross, blasting him for failing to warn him about $12,700 in his wife's unreported income.
"Ross knew all along this was missing and I didn't have a clue until he pointed it out in the middle of the audit," the note read. "By that time it had become brutally evident that he was representing himself and not me."
Reached at his office hours after the crash, Ross confirmed to ABCNews.com that a man with the same name as Joe Stack was a client of his last fall and that Stack did fire him as an accountant after he was audited. They had worked together for about a year.
"I'm shocked," Ross said after being told that not only was Stack being eyed as the suspect in the crash, but that Ross himself was named in the apparent suicide note.
"Wonderful," he muttered shortly after.
Ross said he knew very little about Stack or his wife, only that they seemed like regular clients.
"I really didn't know the man," Ross said. "You have people that are annual type of clients. You see them once a year."
The domain service provider for the angry letter is Tucows, Inc., based in Toronto. The page hosting the suicide note appears to have been last updated today at 10:12 a.m. right around the time of the crash. Data shows the author apparently began work on the note two days ago.
The note detailed attempts to get ahead in life and the setbacks that always seemed to follow, the never realized dream of becoming a prosperous independent engineer, a divorce, the dwindling of his retirement funds.
"If you're reading this, you're no doubt asking yourself, 'Why did this have to happen?'' he wrote. "The simple truth is that it is complicated and has been coming for a long time."
Neighbor Natalie Kunkel told ABC News that she used to socialize with the Stacks and their daughter Margot, swimming with them at a community pool. In the summer of 2008, the family seemed to withdraw and become "noticeably less social."
"I can't believe how he just cracked like that," Kunkel said.
Albert Hutchins, who lives two doors down from Stack but did not know the family, told ABC News that he heard a loud noise and the windows in Stack's house exploded. The fire was so intense, he said, that he could feel the heat just standing on his porch.
Hutchins said he saw the man's wife and daughter leave the house in the morning before the explosion. He confirmed that Stack's wife's name is Sheryl – the same name as the wife mentioned in the "Joe Stack" suicide note.
Austin Plane Crash Directed at IRS
Cullen described the plane as a blue and white Piper Cherokee, a plane he used to use in flying lessons.
"I thought it was going to hit me for a second. It was flying right across the top of the trees. It went right across the building and slammed directly between the first and second floors," he said.
Emergency officials swarmed over the scene, which left the building a smoking hulk of shattered glass. Two people were taken to a hospital and one person was unaccounted for.
The building was located on the 9400 block of Research Boulevard, located along a major highway that runs through Austin.
ABC News' Luis Martinez, Lisa Stark, Matt Hosford, Miriam Smith, Stephen Splane and The Associated Press contributed to this story.