(Ret.) Gen. Mike DeLong has held that Iraqi WMD may have been shipped across the border from Iraq into Syria in the days before the war was launched in 2003:

Two days before March 19, 2003, we saw quite a number of vehicles going into Syria. We could not go after them because we said we'd give Saddam 48 hours. A lot of (Iraqi) leaders went into Syria, and a lot of WMD went into Syria.

According to this New York Sun piece, an Israeli general believes the same thing, although the two accounts differ on timing.