The US Internal Revenue Service is frequently described as the most aggressive, least forgiving, most bullying tax agency in the western world.
The IRS is charged with enforcing a tax code which is incredibly unwieldy and full of traps. The way IRS enforces this tax code is said to frequently result in honest individuals ending up bankrupt or in jail for "transgressions" that they did not even know about.
I do not know this man's background, but quite apparently, the IRS was ruining his life, and he saw no better recourse than to crash his plane into their office building.
Quite possibly, they did, in fact, leave him with no other recourse.
The US tax system must be reformed, and the IRS must get out of the business of destroying people and businesses.