The WH claims it was Assad's regime, although intel hasn't been released yet. So the Syrian government used chemical weapons on their own people.
I'm having a hard time wrapping my brain around this one though. What would Assad have to gain by using NBC's while UN weapons inspectors are in country? If you're going to do it, why on such a small scale? There's two angels that I can see. 1) Assad did it in an attempt to draw in Russian and Iranian support which will follow if the West gets involved. 2) Rebels did it in an attempt to gain aid from the West. There's much to be gained by removing Assad from Syria, both for the West and for Israel.