On May 29, 2003, President Bush proudly trumpeted the supposed discovery of mobile bio-weapons labs in Iraq, declaring, "We have found the weapons of mass destruction." As the Washington Post is now reporting, the President's claim was not only untrue, but the administration knew it was false at the time Bush uttered it.
The Post piece is yet another devastating blow to the White House campaign to retroactively justify the invasion of Iraq. By May 27th, 2003, a team of nine American and British experts unanimously reported that the much-hyped Iraqi trailers had "no connection to anything biological" and were the biggest sand toilets in the world." The team members, all employees working for defense contractors or the Energy Department's national labs, began their work on May 25th, 2003. According to one team member, they concluded "within the first four hours, it was clear to everyone that these were not biological labs." Two days later, they sent their formal, classified report ("Final Technical Engineering Exploitation Report on Iraqi Suspected Biological Weapons-Associated Trailers") to Washington.
Which is where it remains. The Bush administration shelved the report of the "Jefferson Project," as it was called, and continued its claims throughout the summer of 2003. On May 28th, one day after the technical team delivered its unanimous report, the CIA and DIA jointly issued a report ("Iraqi Mobile Biological Warfare Agent Production Plants") ignoring their findings and stating their confidence that the trailers were used for "mobile biological weapons production." By June, Secretary of State Powell, who had vigorously made the case for the existence of the mobile bio-weapons labs during his February 2003 presentation to the United Nations Security Council, declared the American "confidence level is increasing." In September, Vice President Cheney declared the Iraqi trailers "mobile biological facilities" capable of producing smallpox and anthrax.
As it turns out, not so much. By October 2003, Iraq Survey Group head David Kay, who had not seen the classified report, reported to Congress that the ISG found no banned weapons in Iraq and could not verify the potential bio-warfare uses of the trailers. The final Duelfer Report from the Iraq Survey Group in October 2004 concluded definitively that the trailers were not in fact rolling bio-weapons labs:

ISG thoroughly examined two trailers captured in 2003, suspected of being mobile BW agent production units, and investigated the associated evidence. ISG judges that its Iraqi makers almost certainly designed and built the equipment exclusively for the generation of hydrogen. It is impractical to use the equipment for the production and weaponization of BW agent. ISG judges that it cannot therefore be part of any BW program.

The Bush administration, of course, already knew that. In fact, the White House knew it days before President Bush proclaimed in May 2003, "we have found the weapons of mass destruction."
For a complete archive of documents related to Iraq pre-war intelligence and weapons fo mass destruction, including the Iraq Survey Group, the Silberman-Robb Commission Report and the Senate Select Committee on Intelligence Report, visit the Perrspectives Iraq WMD and Intelligence Resource Center.