If one wants a smoking gun, the test site is the obvious answer. The Iraqis tested a device, and have been seeking to construct duplicate devices while trying to develop a larger device ... and they may have already succeeded in that endeavor, but haven't tested it nor do they need to since the specs would have been proven with the initial test successfully completed (as a detonator for the larger version).
Regarding a smoking gun, there are several already billowing : the training base 80 kilks south of Baghdad, the sponsorship for Palestinian and Hamas terrorist activities and successes, the Anthrax genetically linked to the supply we sent to Iraq during the Iran-Iraq war, the 1993 attack on the WTC, the connection between Iraqi Intelligence chiefs and Atta, the ... well, you get the gist.