A long-serving Internal Revenue Service employee died this week when a pilot with a grudge against the federal tax collection agency flew his plane into a building in Texas, his family said.

Authorities investigating the crash in Austin have positively identified the remains of Vernon Hunter, 68, said family spokesman Larry McDonald.

Mr Hunter had been missing and presumed dead since Thursday, when software engineer Andrew Joseph Stack III slammed his plane into the building where Mr Hunter worked as a manager for the IRS.

Mr Hunter's son, Ken, said he assumed the worst after not hearing from his father within an hour of the crash, which set fire to the black-glass building that houses offices where nearly 200 IRS employees work. Mr Stack was the only other person to die in the crash, which also injured 13.

Mr Stack, 53, lashed out at the IRS in a ranting manifesto posted on a website shortly before Thursday's attack, claiming the government and the tax code robbed him of his savings and derailed his career.

"It sounds like it's from some other person," Samantha Dawn Bell, Stack's daughter from his first marriage, told The Associated Press in an interview from her home in Norway.

"It's not him. The letter itself sounds like it's coming from a different person. It didn't sound like it came from him."

In the note, Mr Stack said he realised "violence not only is the answer, it is the only answer",

He apparently set fire to his home before taking off from an airport 30 miles (50km) north of the Texas capital. His current wife and daughter were not at home, but have been left homeless by the blaze.

"Words cannot adequately express my sorrow or the sympathy I feel for everyone affected by this unimaginable tragedy," Mr Stack's wife, Sheryl, said in a statement released yesterday.

Federal law enforcement officials are trying to determine if Mr Stack put anything in the plane to worsen the damage. One law enforcement official also said they were looking into whether a marital dispute precipitated the attack.