Federal law enforcement officials are looking into the possibility that a plane crash into an Austin, Texas, IRS building was intentional.
Pilot Joseph Stack's small plane slammed into the seven-story office building for federal tax employees just before 10 a.m., Thursday, creating what eye witnesses called a "50-foot fireball."
Before taking off, a 10-page anti-government message linked to Stack was posted online. The letter, dated for Thursday, lists problems with the Internal Revenue Service and says "violence not only is the answer, it is the only answer."
"I have had all I can stand," he wrote. "I choose not to keep looking over my shoulder at `Big Brother' while he strips my carcass." The letter was signed "Joe Stack, 1956 to 2010."
All but one of the 190 workers in the building have been accounted for. Two people were taken to the hospital.
"I heard someone yell and I looked up and it was just a burst of flames outside the window," a worker who was two stories above the crash said.
Witnesses in nearby buildings also felt the impact. Local officials stressed the crash was an isolated incident.
"I know the number one fear that's coming to everybody's mind is, was this an act of terrorism and is the country, the city, the region in danger?" Austin Police Department Chief Art Acevedo said. "And I can tell you categorically that there is no cause for concern from law enforcement or a terrorism perspective."
An act of terrorism or not, the crash brought back scary memories.
"When I heard a plane was flying into the building after 9/11, you don't have any time to mess around when somebody says that you get moving," one resident said.
Investigators also said Stack apparently set his house on fire before the suicidal flight.
White House Press Secretary Robert Gibbs said President Obama was briefed by counterterrorism adviser John Brennan shortly before he left for a trip to Colorado and Nevada.
He added that the Department of Homeland Security is investigating all angles of the crash and its cause, but that it "does not appear" to be terrorism.