Reply #17: because Hussein Kamel, Saddam's son in law, told them

[librechik]

he was in charge of WMD and nukes for Saddam, and he was there personally when the substances and devices were all destroyed under UN watch. When he defected to the US in 96, he was interviewed

http://middleeastreference.org.uk/kamel.html

It's all right there. And if you don't believe the guy in charge of Saddams's WMDs that he destroyed them believe the fact that Saddam lured him back to Iraq and executed him as soon as he found out.

here's a snip:
"Kamel specifically discussed the significance of anthrax, which he portrayed as the "main focus" of the biological programme (pp.7-8). Smidovich asked Kamel: "were weapons and agents destroyed?"

Kamel replied: "nothing remained".

He confirmed that destruction took place "after visits of inspection teams. You have important role in Iraq with this. You should not underestimate yourself. You are very effective in Iraq." (p.7)"