Well, on the one hand you have this:
On the other hand, it seems the majority of attacks, the vast majority, have been directed at non-government forces. There are no records of confirmed Sarin attacks by rebels since 2013 which is consistent with looting supply dumps in the initial madness of the war. Since 2013 most attacks have been with Chlorine.
I suspect that the identification of Sarin in this case has a lot to do the reports immediately after the attack which mention nothing of odour.
In any case, there's no reason to believe it's not the regime.
It's also worth noting the Syrian Air Force continues to bomb the town - suggesting there's a reason they targeted it with gas, possible a high-value target has gone to ground there.
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