The 2003 Iraq invasion had nothing to do with warnings from informants about state secrets.
The idea very idea that there was any concern about Iraq's capability to wage war is a joke. Iraq was pretty well softened up by no fly zones and sanctions, so as to be sufficiently anemic, and decapitating the incumbent dictator for life (literally) was mostly just sour grapes for him going off script, and besmirching the sanctity of Kuwait.
It was gloves off for Iraq, as soon as the 9/11 hijackings unfolded. Literally next month people were whispering about Iraq, even though Afghanistan was well understood as the official point of origin for the attacks.