The Organisation for the Prohibition of Chemical Weapons (OPCW) (Note 1) acknowledged in legal filings that it had concealed evidence that it had gathered relating to an alleged chemical attack by the Syrian Arab Air Force in Douma, Syria, on 7 April 2018, according to a document published by the Grayzone.

The allegation was that Syrian Arab Air Forces helicopters dropped two canisters containing reactive chlorine from the air over Douma, killing 43 people. Footage and images from the scene showed victims with profuse foaming around the mouth, which later became part of the claim that chlorine had been used as a chemical weapon.

In response to the incident, the United States, the United Kingdom and France launched military strikes against Syria on 14 April 2018. The three governments said the strikes targeted facilities linked to Syria’s chemical weapons programme. Syria denied that its forces had used chemical weapons in Douma.

The OPCW sent a fact-finding mission (FFM) to investigate. The team first visited one of the alleged sites in Douma on 21 April 2018 to examine whether chemical weapons had been used. It consulted German military toxicologists on 6 June 2018, who, according to documents published by WikiLeaks and statements attributed to former OPCW inspector Brendan Whelan, concluded that the victims’ symptoms were not consistent with chlorine gas exposure.

The physical evidence was also disputed. A leaked engineering assessment attributed to former OPCW official Ian Henderson concluded that the two canisters found at the scene were more likely manually placed than dropped from the air. This challenged the allegation that the cylinders had been delivered by Syrian Arab Air Forces helicopters.

However, the OPCW’s final FFM report, released on 1 March 2019, did not include the German toxicology assessment or Henderson’s engineering conclusion. Instead, it concluded that there were reasonable grounds to believe a toxic chemical containing reactive chlorine had been used as a weapon. The report also stated that no nerve agents or related chemical traces were detected in environmental or plasma samples tested.

The exclusion of those assessments later became central to a labour dispute between the OPCW and Whelan before the Administrative Tribunal of the International Labour Organization (ILOAT). According to the Grayzone, OPCW legal filings in that case acknowledged that the toxicology material had been withheld from the final public report. Former inspectors have also alleged that the United States and allied governments applied pressure to the OPCW to manipulate its key findings.

Note 1: The Organisation for the Prohibition of Chemical Weapons (OPCW), established in 1997, is a treaty-based international organisation that serves as the implementing body for the Chemical Weapons Convention (CWC). Its core mission is to permanently eliminate chemical weapons and prevent their re-emergence globally.

Learn more about Syrian conflict → Syria: Growing humanitarian crisis

Learn about the US and UK’s use of toxic chemicals in Iraq → Iraq: The toxic legacy of Fallujah

OPCW headquarters in The Hague (Photo: OPCW / Flickr [CC BY-NC-ND 2.0])