From the Miami Herald:
A new study suggests the U.S. intelligence assessments of the August 2013 chemical weapons attack outside Damascus, Syria, were flawed. The study says the design of rocket used in the attack, its likely payload and its possible trajectories show that it would have been impossible for the rocket to have been fired from inside areas controlled by the Syrian government.Obviously, if Assad's troops didn't launch the rocket, then the rocket likely came from rebel groups; which, in turn, means that those groups have Sarin nerve gas.
... The report’s authors admit that they deal only with one area of the attacks, the eastern suburb of Zamalka, where the largest quantity of sarin was released that night. They acknowledge that smaller rockets likely used in areas southwest of the capital could have come from government-controlled territory.
Relying on mathematical projections about the likely force of the rocket and noting that its design – some have described it as a trash can on a stick – would have made it awkward in flight, Lloyd and Postol conclude that the rocket likely had a maximum range of 2 kilometers, or just more than 1.2 miles. That range, the report explains in detail, means the rockets could not have come from land controlled by the Syrian government.
To emphasize their point, the authors used a map produced by the White House that showed which areas were under government and rebel control on Aug. 21 and where the chemical weapons attack occurred. Drawing circles around Zamalka to show the range from which the rocket could have come, the authors conclude that all of the likely launching points were in rebel-held areas or areas that were in dispute. The area securely in government hands was miles from the possible launch zones.