Re: Maybe there is some confirmation bias involved. Investigations do tend suffer from this when gathering evidence....meaning they will throw out evidence that could lead to exoneration as opposed to evidence that would lead to implication of someone they are initially against and moreso someone who has a certain reputation. There is a likelihood that Assad did use gas in 2013 during the Obama Administration, as that was heavily investigated and confirmed by most of the international community, not just Zionist allies. Russia even agreed upon a deal that would reduce Syria's chemical weapons. After that, though, it is possible that subsequent attacks were carried out by ISIS knowing that Assad's previous actions using chemical weapons would parlay into future investigations having a certain amount of confirmation bias implicating him, no matter if he did it or not. Remember, ISIS did not go to Syria help the opposition. ISIS declared a worldwide caliphate and was going destroy everyone who didn't bow down to their brand of Islam(Sharia Law). They are just as much against Assad as they are against the Syrian people and have targeted and killed lots of civilians in Syria without flinching an eye
One thing is for sure, there hasn't been as strong of an investigation of ISIS's involvement in these chemical weapons attack as there has been an investigation of Assad's involvement.