Weren't there also RUSSIANS in the trucks?
The Russians had a policy for recovering 'illegal' arms and hiding them should the purchaser have to surrender to a greater force.
The stockpiles in IRAQ were quickly moved by a consortium of 'russians' (an easy description for far east organized crime) to Syria for storage in safe , underground facilities.
We watched them do it. We even helped. Better for the weapons to be secured, than for one of Saddam's sons to decide to use it.