The justifications for war are spelled out quite clearly in UN Resolution 1441.
U.N. Security Council Resolution 1441
I won't quote the whole thing but here are some pertinent clauses and phrases ....
~ Deploring the fact that Iraq has not provided an accurate, full, final, and complete disclosure, as required by resolution 687 (1991), of all aspects of its programmes to develop weapons of mass destruction and ballistic missiles with a range greater than one hundred and fifty kilometres ...~ Deploring further that Iraq repeatedly obstructed immediate, unconditional, and unrestricted access to sites designated by UNSCOM and IAEA, failed to cooperate fully and unconditionally with UNSCOM and IAEA weapons inspectors, as required by resolution 687 (1991), and ultimately ceased all cooperation with UNSCOM and the IAEA in 1998, ...
~ Deploring also that the Government of Iraq has failed to comply with its commitments pursuant to resolution 687 (1991) with regard to terrorism, pursuant to resolution 688 (1991) to end repression of its civilian population and to provide access by international humanitarian organizations to all those in need of assistance in Iraq, and pursuant to resolutions 686 (1991), 687 (1991), and 1284 (1999) to return or cooperate in accounting for Kuwaiti and third country nationals wrongfully detained by Iraq, or to return Kuwaiti property wrongfully seized by Iraq, ...
There is much more in that resolution, much of it having nothing at all to do with WMD, that constitutes reason for removing the regime of Saddam Hussein.