Unseen World!

Smoke billows from a building after a small private plane crashed into the building in Austin, Texas Photo: AP

Joseph Stack left a six-page suicide note in which he railed against the Internal Revenue Service, the US federal tax agency.

He wrote: "I am finally ready to end this insanity. Well, Mr Big Brother IRS man let’s try something different. Take my pound of flesh and sleep well.

"There was a storm raging inside me. Desperate times call for desperate measures. We are brainwashed to believe there is freedom in this land."

In his suicide "manifesto," which he posted on his own website, Stack also railed against Wall Street bankers, the Catholic Church, President George W Bush and the health care system.

The software engineer detailed how he had spent $5,000 (£3,000) and 1,000 hours of his time writing to senators and congressman about taxes and how he lost his retirement savings for the second time in the 1990s.

Stack crashed the four-seater aircraft into a seven-storey building which housed 199 IRS employees in the state capital Austin.

It created a huge fireball and at least two people in the building were injured, with one unaccounted for.

An FBI office was located next door to the tax office and NORAD, the North American Aerospace Defense Command, scrambled two F-16 jets from Houston amid fears of a terrorist attack.