What on earth is going on at Newsweek? An article posted on its website earlier this month wrongly claimed that James Mattis, the US defense secretary, had said there is no evidence of the Assad regime using the nerve agent sarin against its people.

The claim attributed to Mattis was demonstrably untrue, as could be seen from the published transcript of his remarks. Despite that, the article remains on Newsweek's website – uncorrected – and continues to be promoted on social media by conspiracy theorists and Assad apologists.

It might be assumed that Newsweek, having got its fingers burned once, would – at the very least – think twice before accepting more articles from the same author. But no. On Saturday there was another one, this time asking: "Where's the evidence Assad used sarin gas on his people?"

The author of both articles was Ian Wilkie, described by Newsweek as "an international lawyer and terrorism expert and a veteran of the US Army (Infantry)". He is said to be is working on a book, "Checkmate: Jihad's Endgame", about the potential uses of weapons of mass destruction by terrorists.

The problem with the first article was that Wilkie drew sweeping conclusions based on what he thought Mattis had or had not said, without bothering to check what he actually said (for details see previous blog post).

Wilkie's latest article begins reasonably enough by emphasing the importance of evidence when discussion chemical weapons in Syria but then completely ignores the vast body of evidence compiled by the UN and the Organisation for the Prohibition of Chemical Weapons – much of it based on laboratory tests.

Instead, he suggests the only available evidence comes from "the quasi-paid promotional material of regime change boosters" and regurgitates a long-discredited claim about bombs accidentally hitting chemicals stored on the ground.

Perhaps Newsweek imagines that articles of this sort contribute to public debate, but they don't. At least, not informed debate.