Thread's gone a bit quiet since John Kerry made his statement and apportioned blame:
US Secretary of State John Kerry has condemned what he termed the "moral obscenity" of the Syrian government's use of chemical weapons against its own people.
"What we saw in Syria last week should shock the conscience of the world. It defies any code of morality," Mr Kerry said at a news conference on Monday.
"Make no mistake," he continued, "President Obama believes there must be accountability for those who would use the world's most heinous weapons against the world's most vulnerable people."
The US administration had additional information about the attack that it would make public in the days ahead, he added.
Furthermore, this article would suggest the US knows that the rebels do not have chemical weapons nor the capacity to deliver them, mainly because the Assad regime was ensuring they don't fall into the hands of the rebels.
http://edition.cnn.com/2013/08/26/opinion/syria-chemical-weapons-opinion/?hpt=hp_c1
I'd hazard a guess that despite requiring the UN inspection teams to provide concrete proof for the naysayers, their operatives in the field (combined with satellite imagery) have gleaned more than enough evidence militarily of use of the weapons by the Assad regime. That evidence will be presented to the world very shortly.