They pulled out a grenade, and they -- anyway, somehow, they started fighting, starting with a grenade, and then one of them grabbed a (inaudible) from one of the army forces.

CNN: Transcript of John Walker interview

The WMD law also applies to "any national of the United States who, without lawful authority, uses or threatens, attempts, or conspires to use a weapon of mass destruction outside of the U.S.." In March 2013, former U.S. soldier Eric Harroun was charged under this part of the statute for allegedly conspiring to use a rocket propelled grenade while fighting with an al Qaeda affiliated group in Syria.

CNN: WMD: From A-bombs to pressure cookers