Authorities Rule Arson Caused Fire at Pilot's Texas House

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Authorities in Texas have ruled arson is the official cause of the fire that destroyed the house belonging to the man who flew his plane into an office building.

Austin Fire Department spokesman Andre de la Reza said Thursday that the Feb. 18 blaze was intentionally set. Investigators say Joseph Stack started the blaze, drove to a nearby airport and then flew his single-engine plane into the complex that houses offices of the Internal Revenue Service. The crash killed Stack and IRS employee Vernon Hunter.

SLIDESHOW: Small Plane Crashes Into Austin Office Building

Authorities later found a rambling manifesto from Stack in which he described a long-smoldering dispute with the IRS and a hatred of the government.

The family's accountant has confirmed that the Stacks were in the middle of an audit for reportedly failing to report income.