Note the "mushroom cloud over a US city away" vs. the 1,400 dead bodies from the gas cloud that was actually used. I don't have an intelligence clearance, but I'm willing to believe that either the intelligence community has abundant evidence to support their position, or they are out-right lying to us, and I see no benefit to them or anyone if they are lying.
The UN report released today confirmed evidence of a sarin attack and noted impacted rocket remnants as evidence. If the rebels used sarin, wouldn't they have set off a stationary bomb loaded with the stuff in the area they wanted to affect? Because it doesn't seem that they have the technical ability or training to launch a rocket and know where it's going to hit.
If and when the Syrian regime gives up their CW, will that convince you it was them?
Forensic Details in U.N. Report Point to Assad’s Use of Gas
"Obamacare delenda est"
I would also say that the rebels have had the capability to do the attack as they had surface to surface missiles.
Reported August 23, 2013:
"The Free Syrian Army - as well as the Al-Qaeda affiliated al-Nusra Front and other groups - have also been using increasingly potent captured artillery. This has included Grad surface-to-surface rockets analysts say were vital to the Islamist-led push into Latakia." (Syria government, rebels ramp up conventional weapons use | Reuters)'
Reported in July 2013:
"These antiaircraft, antitank, and surface-to-surface weapons are in the hands of both the Free Syrian Army (FSA), which is considered relatively moderate, and the local and global Islamist forces, and are being used to combat aircraft, armored vehicles, and regime bases." (Syrian Rebels Developing Rocket, Missile Capabilities To Combat Aircraft, Tanks, And Ground Targets)
"And in the end, we were all just humans, drunk on the idea that love, only love, could heal our brokenness."
They've already got John McCain on the payroll. It's not surprising that they've got a few less prominent people like ecofarm too.