The claim of chemical weapon use now seems less certain: the New York Times prepares for another Judith Miller scandal

"American intelligence agencies have medium to high confidence that chemical weapons have been used in Syria, but it is not completely clear who was using them.  The Obama administration recognizes that the rebels and their supporters have an incentive to assume or even exaggerate the use of such weapons because it may be the one thing that could draw in direct Western military intervention against Mr. Assad. The rebels have access to information online about the effects of the weapons, so they may know what symptoms to describe to make their claims seem real."