Lying or mistaken
I think it's fairly obvious that any administration that would deliberately invent evidence before the war, and be able to effectively do so, would have done the same thing afterwards in Iraq, manufacturing proof of Saddam's weapons programs.
The most telling evidence that the administration was sincere was that they were just as astonished at the lack of active programs as anyone else.
Most people forget that if we had not invaded, and gained complete access to things that the U.N. would never have seen in a hundred years, we would still be guessing at what Saddam was doing.
As it is, the inspection reports are clear that Saddam intended to resume WMD work as soon as the heat was off.
From the evidence available through the actions and statements of a range of Iraqis, it seems clear that the guiding theme for WMD was to sustain the intellectual capacity achieved over so many years at such a great cost and to be in a position to produce again with as short a lead time as possible—within the vital constraint that no action should threaten the prime objective of ending international sanctions and constraints.
Saddam continued to see the utility of WMD. He explained that he purposely gave an ambiguous impression about possession as a deterrent to Iran. He gave explicit direction to maintain the intellectual capabilities. As UN sanctions eroded there was a concomitant expansion of activities that could support full WMD reactivation. He directed that ballistic missile work continue that would support long-range missile development. Virtually no senior Iraq; believed that Saddam had forsaken WMD forever. Evidence suggests that, as resources became available and the constraints of sanctions decayed, there was a direct expansion of activity that would have the effect of supporting future WMD reconstitution. (italics in original)
The last part of this letter shows that if either 9/11 had not happened, or if Iraq had been left alone while America was occupied with Afghanistan, Saddam would eventually have begun WMD work again. The article is clear that U.N. inspections resumed at all only because of the imminent threat of U.S. military force. Otherwise, Saddam would now be playing "rope-a-dope" with the U.N. just like Iran, while rebuilding his WMD capacity. With Iran next door doing the same thing. If that's what people call "stability in the Middle East," the word may need redefinition.