A top US biodefence researcher committed suicide just before being charged over the anthrax mailings that traumatised America after the September 11 2001 terrorist attacks.

Preliminary tests of a white powder discovered in a US Senate office building in Washington were positive for the potentially deadly poison ricin, police said.

The Pentagon has finally discovered evidence of weapons of mass destruction - buried in a US Army base 50 miles from Washington DC.

The US Justice Department is preparing to give lie detector tests to hundreds of government workers at two centres where anthrax is stored, hoping to identify suspects in the letter attacks.

As lawmakers take a Thanksgiving holiday week break, two of the three Senate office buildings in Washington are set to reopen after being swept for anthrax contamination. The third will remain closed.