What was known about Saddam Hussein's use of weapons of mass destruction prior to the US invasion in 2003?

General Reference (not clearly pro or con)
Rolf Ekéus, former United Nations Weapons Inspector, wrote in a June 29, 2003 Washington Post article titled "Iraq's Real Weapons Threat":

"Chemical weapons were used by Iraq in its war against Iran (1980-88). Arguably that use had a decisive effect on the outcome: It saved Iraq from being overwhelmed by a much larger Iranian army. Furthermore, Iraq made use of chemical bombs in air raids against the Kurdish civilian population in northern Iraq. Nerve gases, such as sarin, and mustard gas immediately and painfully killed many thousands of civilians. More than 100, 000 later died or were crippled by the after-effects."

June 29, 2003 - Rolf Ekéus 

The US Army Medical Research Institute of Chemical Defense (USAMRICD) stated in its July 2000 edition of the "Medical Management of Chemical Casualties Handbook":

"Widely publicized reports of Iraqi use of chemical agents against Iran during the 1980s led to a United Nations investigation that confirmed the use of the vesicant mustard and the nerve agent GA [synthesized tabun, an extremely toxic organophosphate compound]. Later during the war, Iraq apparently also began to use the more volatile nerve agent GB, and Iran may have used chemical agents to a limited extent in an attempt to retaliate for Iraqi attacks. Press reports also implicated cyanide in the deaths of Kurds in the late 1980s."

July 2000 - Medical Management of Chemical Casualties Handbook (2 MB)  
US Army Medical Research Institute of Chemical Defense (USAMRICD) 

Human Rights Watch, a non-governmental organization, stated in their Feb. 20, 2003 briefing paper titled "International Humanitarian Law Issues in a Potential War in Iraq":

"Although Iraq has repeatedly claimed that it currently has no weapons of mass destruction, it has used chemical weapons in the past against both combatants and civilians. The Iraqi army repeatedly used chemical weapons against Iranian armed forces between 1983 and 1988. Furthermore, it used chemical weapons against Kurdish civilians at Halabja in 1988, killing up to 5,000 people, and on some forty documented occasions that year during the Anfal genocide against Iraqi Kurds. These previous uses of chemical weapons violated the 1925 Geneva Protocol that prohibited the use of chemical weapons."

Feb. 20, 2003 - Human Rights Watch (HRW)