CNN is an excellent source to discount the professor. Not.
the link isn’t to a cnn article. It’s to The Hague’s OPCW report hosted at cnn. Which is also at the opcw website - if you know how to dig for it.
Also at the opcw website that you’ll also have to dig for, is the Dec ‘16 recommendation that, much like Iraq, Syria was to immediately submit to site inspections, hand over flight logs for previous confirmed attacks in 2014/15/16, blah blah. Not exactly something Assad wanted to happen for many reasons.