Until the United Nations inspectors make their report we will not know for certain whether the Syrian army or the Syrian rebels used poison gas.
Points to consider:
1. People treating those affected by the poison gas were
not using protective clothing, those giving aid to the
dying would have also died from contact with those
affected if the gas used was military grade.
2. The Syrian rebels want additional outside assistance
& Muslim extremists among them could have used the
gas hoping the international community would
intervene blaming the Syrian army.
3. The Syrian army was/is well aware of the fact that
using poison gas would invite international intervention
& clearly knows it is in their best interest to avoid
international intervention.