The story that the Syrian government used chemical weapons on its own population at Douma was always suspect. From Caitlin Johnstone at medium.com:

The Courage Foundation, an international protection and advocacy group for whistleblowers, has published the findings of a panel it convened last week on the extremely suspicious behavior of the Organization for the Prohibition of Chemical Weapons (OPCW) in its investigation of an alleged chemical attack in Douma, Syria last year. After hearing an extensive presentation from a member of the OPCW’s Douma investigation team, the panel’s members (including a world-renowned former OPCW Director General) report that they are “unanimous in expressing our alarm over unacceptable practices in the investigation of the alleged chemical attack in Douma, near the Syrian capital of Damascus on 7 April 2018.”
I’ll get to the panel and its findings in a moment, but first I should provide some historical background so that readers who aren’t intimately familiar with this ongoing scandal can fully appreciate the significance of this new development.