AUSTIN, Tex.  Leaving behind a rant against the government, big business and particularly the tax system, a computer engineer smashed a small aircraft into an office building where nearly 200 employees of the Internal Revenue Service were starting their workday Thursday morning, the authorities said.

The pilot, identified as Andrew Joseph Stack III, 53, of north Austin, apparently died in the crash, and one other person was unaccounted for. Late Thursday, two bodies were pulled from the site, though the authorities would not discuss the identities of those found, The Associated Press reported. Two serious injuries were also reported in the crash and subsequent fire, which initially inspired fears of a terrorist attack and drew nationwide attention.

But in place of the typical portrait of a terrorist driven by ideology, Mr. Stack was described as generally easygoing, a talented amateur musician with marital troubles and a maddening grudge against the tax authorities.

“I knew Joe had a hang-up with the I.R.S. on account of them breaking him, taking his savings away,” said Jack Cook, the stepfather of Mr. Stack’s wife, in a telephone interview from his home in Oklahoma. “And that’s undoubtedly the reason he flew the airplane against that building. Not to kill people, but just to damage the I.R.S.”