When he knew that he was going down, he could have simply destroyed the chemical/biological material. You simply add a mix to the chemical/biological stuff to change its form and make it non-lethal. If these things were stored in a lab it would take a few seconds for them to perform such an act, before fleeing Baghdad. Then even when the U.S. finds the stuff they can't say this is nerve gas or anthrax since they changed what they were. They don't even need to bury the shit anywhere hard to find.