there have been cases in Syria where footage of the aftermath of a chemical weapon attack was most probably staged. that's to say the Russian envoy to the UN presented witnesses who were present and filmed at the time
also, on a slightly different vein there was a lot of drama from the body sent to investigate the site: a leading member of the team resigned alleging he had been told to keep the narrative
(I'm going by memory here, probably best to check and see for yourself)
but, you only really have to go back to the infamous war of the world's broadcast, or even the BBC spaghetti tree thing to see how easy it is to influence masses with little effort and also how susceptible people can be, and on many levels are expected to be
the Russians are also alleging bad craic going on with their pows. apparently some footage has been circulating which shows summary executions roadside
apparently the footage has been verified.
but to answer your question. most probably
U.S. military stated the two previous chemical weapon attacks in Syria in the last 4 years were most likely staged. Both happened on the eve of President Trump removing troops from the country. Surely just coincidental...