UPDATE: Officials investigating Texas crash as a crime

AUSTIN, Texas — Police in Austin, Texas, say the crash of a small plane into a building that houses the Internal Revenue Service is an isolated incident and "there is no cause for concern" about terrorism.

U.S. law enforcement officials say they are investigating whether the crash was an intentional act by the pilot that was aimed at the IRS. They spoke on condition of anonymity because the investigation is continuing.

Austin fire officials said one person who was scheduled to be at work Thursday is still unaccounted for, and two people were taken to a hospital. Their conditions and identities were not known.

FAA spokesman Lynn Lunsford says the pilot didn't file a flight plan.

The Associated Press reported from Washington that a law official identified the crash pilot as Joseph Stack and that he had an "angry anti-IRS" Web page.

Web site NowPublic reported that the domain being cited is registered to Joe Stack, according to this registry information.

The Associated Press and Missourian Staff contributed to this report.