According to the OPCW, its Fact-Finding Mission (FFM) conducted a number of on-site visits and "analyzed a range of inputs including witness testimonies, environmental and biomedical samples analysis results, toxicological and ballistic analyses, and additional digital information from witnesses."
"Regarding the alleged use of toxic chemicals as a weapon in Douma, the evaluation and analysis of all the above-referenced information gathered by the FFM provide reasonable grounds that the use of a toxic chemical as a weapon has taken place on April 7, 2018. This toxic chemical contained reactive chlorine. The toxic chemical was likely molecular chlorine," the report said.
The United States, backed by France and the United Kingdom, promptly fired over 100 missiles on what they called the Syrian government's chemical weapons sites without waiting for the results of a probe conducted by the OPCW.
The Russian Foreign Ministry has said that the claims about the alleged use of toxic chemicals by the Syrian government were aimed at justifying external military action.