So, Ghouta.
What we know for a fact is that some sort of chemical warfare took place there.
It is not known who used the gas. It is not even known for certain what kind of gas was used, which would be important for determining who could have possessed and therefore used it.
Assad, Russia and Iran staunchly support the thesis that the rebels were the ones to use it. Syria does not deny the offensive on Ghouta, but Syrian television has reported that Syrian troops nearly suffocated when entering the city.
France, the US and Turkey say with conviction that it was Assad who used the gas, and that a red line has been crossed. The US wants to send warships, while France says that any sort of action should not involve boots on Syrian ground.
Firas Abi Ali, the head of the Middle East and North Africa country risk team for IHS Global, has, upon being asked by Al Jazeera, stated that he believe the attack was conducted by someone in the Baath party's inner circle, in order to force Assad to keep a hard line.
On other news stations, I have read a between the lines interpretation that it was the rebels staging a false flag operation to make it look like it was Assad's doing, to force foreign support.
To be quite honest, I find each of these explanations equally plausible.