Damn..I wish there was a way we could prove this!
We can. According to Loftus (I know, I know), the DIA photographed them. Maybe Assad would turn them over. I know that's naive, but it could happen. Probably not.
Common sense would tell us that the WMD's were moved to another country as Hussein had ample time (with all the UN stalling and game playing) to move stuff where he wanted it.