Here's another video that some claim is proof that the opposition rebels were responsible. Eretz Zen Channel (Assad supporter) has the following explanation:
This video footage that recently surfaced shows jihadi militants from the Islam Battalion that operates in the Damascus suburb of Eastern Ghouta and led by Zahran Alloush launching an operation called "al-Reeh al-Sarsar" (Almighty Wind) on the Damascus suburb of al-Qaboun in Eastern Ghouta at the early morning of Wednesday, August 21, 2013.But was it staged? Some think it might be, but no-one knows for sure. Bottom line, nothing and no-one can be trusted.
The video shows men wearing gas masks and firing an artillery shell while shouting Allahu Akbar! The name of 'al-Reeh al-Sarsar' is coincidentally the name of the "chemical brigade" that posted videos threatening the use of chemicals on Syrian government supporters, especially Alawites, while testing the chemicals on rabbits.
Truthloader has more on the above allegations at the beginning of their latest video, along with claims that the Syrian government handed over proof to Russia that the jihadis were involved.