Seems he'd had a run in with the IRS that cost him $40K which also interfered with his retirement funding. He saw the big boys getting bailed out after he'd been screwed over and decided to strike back in a forceful manner.
http://www.myfoxhouston.com/dpp/news/local/100218-austin-pilot-manifesto
Video of him playing in a band.
http://www.myfoxhouston.com/dpp/news/texas/100219-video-joe-stack-plays-in-band
Texas pilot decided to file his income tax return with the IRS by airmail.
http://www.cnn.com/2010/US/02/18/texas.plane.crash/

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