Facts

• The Organization for the Prohibition of Chemical Weapons (OPCW), the world's chemical weapons watchdog, released a report on Friday blaming the Bashar Al Assad-led Syrian Air Force for the alleged April 2018 chlorine attack in the city of Douma.
• Investigators allege that at least one helicopter of the Syrian Elite Tiger Forces Unit dropped two cylinders containing toxic chlorine gas on two apartments in a civilian-inhabited area nearly five years ago, killing 43 individuals and affecting dozens more.
• They stated there were "reasonable grounds" to reach this conclusion after examining 70 environmental and biomedical samples, 66 witness statements, and other data, including forensic analysis, satellite images, gas dispersion modeling, and trajectory simulations.
• The watchdog claims to have carefully assessed alternative theories for what happened but rejected all of them, including Syria's claim that the attack was staged and bodies of people killed elsewhere in Syria were taken to Douma.
• Using chlorine as a weapon is banned under the Chemical Weapons Convention, which Syria ratified in 2013 – two years into the war – as well as under customary international humanitarian law. Syria has rejected the report as "false," claiming it "lacks scientific proof."
• The Douma case has faced controversy, with the OPCW previously being accused by former employees of altering its findings. According to leaked material, the original investigation found some symptoms were "not consistent with exposure to chlorine-containing choking or blood agents," and failed to detect "organophosphorous nerve agents." It further concluded the cylinders were more likely manually placed than dropped from great heights. This was omitted in the final 2019 report.