Maple 01
I don't know what specific int was available, nor do I wish too. However, just from reading Tom Clancy novels I could guess at least two possible sources, Human Int and satellite photos.
With regard to Human Int, it is probably quite easy for a defector to work out what sort of information his 'bebriefers' are looking for, and provide them with it, even without going into specifics, just talk about lots of heavily guarded convoys moving at night which he was ordered not to discuss, etc, etc. The more a defector tells his debriefers what they want to hear the more valuable he is to them and the better treatment he receives.
As for satellite photos. Satellite pass times are easily predictable. It should be quiet easy to set up a 'show for the cameras'. Just get a convoy of lorries to drive into a base at satellite pass time, with a heavy escort and decontamination vehicles present. The lorries could be full of sand, but the guy examining the photos will think differently!
The point is, western intelligence agencies have all looked at the data assuming Saddam had something to hide. What if he didn't, but was, for reasons of his own, trying to make the world still think he actually had WMD? It would be fairly easy I think to provide some evidence for people who were eager to find it.
Why would Saddam want people to think he had WMD when he didn't? Well for that you have to get inside his head, and to do that you need to drop your western preconceptions. To look big in the region perhaps, to keep his own people in check, to make Iran think twice before any actions it might undertake? Who knows, but it might well turn out to be the case.
The point is, if we are going to war on the basis of intelligence it has to be 100% certain, and I don't think this was (although I don't work in Intelligence).
As to the arguement, "would you rather Saddam was still in power?", no I wouldn't, but that isn't the point. Tony Blair sold us on going to war on the basis of the existence and possible use of WMD. If as a nation we are instead going to rid the world of all evil tryants then I had better start packing my bags for a trip to Zimbabwe!!!!!!!!!!