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.
Check out Leopold and Loeb. They wanted to commit the "perfect crime". They killed a classmate just for the thrill of it, to show that they were superior intellects and could get away with it. Pretty remarkable, but a true story. They really bothched the murder and left a lot of evidence, even though they did a lot of planning ahead of time, including creating ficticious sharacters, Morton D Ballard and Louis Mason, to send the police chasing wild goose chases. They even arrested someone, named George Johnson, who matched the fictional name of their fictional killer. Now I know no one has called Sadaam Hussein, George Johnson, but there are enough clues to figure out the real deal here.
Just blow the dust and waiting till you see how the real thing flys.