WASHINGTON (AP) - U.S. law enforcement officials say they are investigating whether the crash of a small plane into a building in Austin, Texas, may have been an intentional act by the pilot.

The officials said authorities are trying to determine if the pilot intentionally targeted nearby office space of the Internal Revenue Service. They spoke on condition of anonymity because the investigation is continuing. A third official said authorities are pursuing reports that the pilot may have been disgruntled with the IRS.

As a precaution, the Colorado-based North American Aerospace Defense Command launched two F-16 aircraft from Houston's Ellington Field, and is conducting an air patrol over the crash area.

The Associated Press reports authorities are trying to determine if the pilot targeted the tax agency.

Assistant Austin Fire Chief Harry Evans says one person is missing and two people were taken to a hospital. Their conditions and identities weren't immediately known.

The crash sent workers fleeing as ceilings crumbled, windows shattered and flames shot out of the building.

Thick black and gray smoke was billowing out of the second and third stories.

Federal Aviation Administration spokesman Lynn Lunsford says the pilot didn't file a flight plan.

IRS worker Peggy Walker was at her desk when the plane crashed.

She says: "It felt like a bomb blew off."

(Copyright 2010 by The Associated Press. All Rights Reserved.)

Officials: Plane crash pilot torched his own house

AUSTIN, Texas (AP) - Officials say they believe a software engineer set fire to his house before taking a small plane and crashing it into an Austin office building.

Officials say Joseph Stack was furious with the Internal Revenue Service, which has an office with nearly 200 employees in the building he crashed into. That set off a raging fire that sent workers fleeing as thick plumes of black smoke poured into the air.

Investigators are looking at an anti-government message on the Web linked to him. The Web site outlines problems with the IRS and says violence "is the only answer."

The house, listed as belonging to Stack, burned in a neighborhood about six miles from the crash site. Two law enforcement officials said Stack had apparently set fire to his home before the suicidal plane flight.

(Copyright 2010 by The Associated Press. All Rights Reserved.)

Official: Plane crash pilot left anti-IRS Web note

AUSTIN, Texas (AP) - A software engineer officials say was furious with the Internal Revenue Service plowed his small plane into an Austin office building housing nearly 200 federal tax employees today.

That set off a raging fire that sent workers fleeing as thick plumes of black smoke poured into the air.

A U.S. law official identified the pilot as Joseph Stack and said investigators are looking at an anti-government message on the Web linked to him. The Web site outlines problems with the IRS and says violence "is the only answer."

Federal law enforcement officials have said they were investigating whether the pilot, who is presumed to have died in the crash, slammed into the Austin building on purpose in an effort to blow up IRS offices. All the officials spoke on condition of anonymity because the investigation was ongoing.

The long note dated today on Stack's Web site says "Violence not only is the answer, it is the only answer" to his past problems with the IRS.

It also says, "I saw it written once that the definition of insanity is repeating the same process over and over and expecting the outcome to suddenly be different. 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."

Read a transcript of the note here

(Copyright 2010 by The Associated Press. All Rights Reserved.)

FBI tentatively IDs Texas plane crash pilot

AUSTIN, Texas (AP) - The FBI has tentatively identified Joseph Stack as the man who crashed his small plane into an Austin building that houses the Internal Revenue Service.

The FBI says the forensic investigation continues to confirm the pilot's identity, and authorities say his body has not yet been recovered.

Authorities told reporters that 13 people were treated after Thursday morning's crash and two remain in critical condition. One person who works in the building remains unaccounted for.

(Copyright 2010 by The Associated Press. All Rights Reserved.)