I also read that Assad says the chemical attack is fabricated. Unfortunately we will never know the truth. With all of the propaganda coming from all sides who knows who was responsible or even if there was an attack. That doesn't matter now, what matters is what happens next.
I quite remember the US fabricating the same thing under President Obama saying Assas used chemical weapons, they whole thing was later revealed to have been fabricated and that the rebels used the chemical weapons and the US knew about it the whole time, just that they wanted an excuse to oust Assad.