How the US found out Assad was using chemical weapons

For those of you who keep suggesting that maybe it was the rebels in Syria who used the chemical weapons... it wasn't (and that's not to say that they wouldn't if they had them) (Hat Tip: Memeorandum).

Last Wednesday, in the hours after a horrific chemical attack
east of Damascus, an official at the Syrian Ministry of Defense exchanged
panicked phone calls with a leader of a chemical weapons