The note was titled "Well Mr. Big Brother IRS Man … take my pound of flesh and sleep well." It detailed 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 read.
Records show two of Stack's software companies were suspended by the state tax board.
"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.
Forensic psychiatrist Dr. Michael Welner told "Good Morning America" that while it may appear that Stack simply snapped under the weight of tax debt, it was clear from the suicide note that this had been brewing for some time.
"This is the kind of crime that's planned for a long time," Welner said. "I wouldn't be surprised to learn that he practiced."
Calling the attack a "crime of rebellion," Welner said it was obvious that Stack had planned the crash to maximize public attention by invoking both the Oklahoma City bombing of a federal building and the 9/11 terrorism attacks.
"I think it's important to distinguish this as a spectacle murder because it's carried out in order to get on the news," he said.
The Federal Aviation Administration told ABC News that Stack did not communicate with air traffic controllers once he got in the air around 9:40 a.m. nor did he file a flight plan.
Officials told ABC News that once a man like Stack decides to plan this type of attack, there is very little they can do to stop it, especially once he's in the air and locked on a target.
Witnesses said Thursday that the plane appeared on a purposeful track, banking sharply as it flew over a major highway directly into the office building.
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.
Stack has been described as quiet. He had lived in his Austin neighborhood with wife Sheryl and their daughter for about three years, having moved from California.
Mechanic Dave Page, who used to work on Stack's plane in California, told ABC News that he was a hard-working guy.
"I think he pretty much, his life was work," he said. "He enjoyed doing what he did. He liked flying his airplane."