A new report from the global chemical weapons watchdog found there are “reasonable grounds to believe” the Syrian air force was behind a 2018 chlorine gas attack on a residential part of rebel-held Idlib province. 

The Organization for the Prohibition of Chemical Weapons (OPCW) concluded that a military helicopter under the control of Syria’s elite Tiger Forces in February 2018 dropped at least one cylinder, dispersing the toxic gas over the Saraqib neighborhood of al-Talil.

There were no casualties in the alleged attack, but OPCW’s investigation confirmed 12 people displayed symptoms consistent with chlorine exposure including shortness of breath, skin irritation, chest pain and coughing. Eleven were treated at a field hospital in the town of Sarmin, as the closest hospital in Saraqib had just been bombed. 

The Hague-based watchdog analyzed samples collected from the contamination site, munition remnants, gas dispersion models and topographic studies. In addition to consulting with forensic experts, investigators also “reviewed thousands of files amounting to more than 400 gigabytes, obtained 44 statements from more than 30 witnesses and considered data related to 18 samples.”