Origins of the samples coming out of Syria cannot be guaranteed

"The problem is, if there is sarin in a sample, where did it come from? Charles Blair of the Federation of American Scientists points out that it would be in the interests of rebel forces to involve the US in their fight against Assad – and the origins of the samples coming out of Syria cannot be guaranteed. Some believe a sarin-tainted sample would be hard to fake. For one thing, the US believes Assad controls all of Syria's CW munitions. But that may not be the only source. When the US had chemical weapons, the army, until 1969, gave out small vials of agents, including sarin, to teach soldiers to recognise their smell – and they were widely distributed. Similar vials used to train Syrian soldiers might have tempted beleaguered rebels."