If the chemical were used by Syrian Army, the cameraman and all others around would be affected by the chemical weapon. We can see that the implementors are the ones who are standing near victims.
for more details:
Exclusive- The sinister game of Chemical Wepaons by terrorists in Syria REFUTED, UNCOVERED!!!
Exclusive-Photo- Al Jazzera, Reuter published the news of massacre in East Ghouta, Damascus one day before the massacre happened.