Assad would be stupid to use chemical weapons close to where the UN observers were staying just a few days after the UN observers arrived.
Getting to the bottom of who used the weapons won’t be easy. With the Brotherhood getting their ass kicked in Egypt, it was time to draw attention somewhere else.
It’s hard to say - could have been either. But it’s interesting that Assad shelled the area a day or 2 after the story broke....trying to cover up evidence & keep the U.N. out?