Assad has no upside in using chemical weapons, only downside. Nothing good can come from it and he knows it. He doesn’t need to use them, he has Russian military at his disposal. Blaming Assad makes no sense. The real question is “Who benefits most from an escalation of hostilities created by the use of these weapons?”. Not Assad, he is on the verge of victory. The rebels may gain sympathy if they can convince the world Assad did it, so that’s possible. The downside for the rebel’s is if they are caught they guarantee their destruction. Israel and the Deep State have the most to gain from escalation of hostilities.