The Organisation for the Prohibition of Chemical Weapons has now published a response to Russian and Syrian criticisms of the investigative work done by its Fact-Finding Mission (FFM).

On 1 March, the FFM issued a report which found “reasonable grounds” for believing a toxic chemical had been used as a weapon in Douma, on the outskirts of Damascus, and suggested the chemical was delivered by two gas cylinders dropped from the air.

Ten days later, Syria sent the OPCW a note verbale containing a series of critical comments and questions. On 26 April, Russia also sent a note verbale disputing the FFM's findings (see previous blog post).

The OPCW doesn't normally engage in public debate about its investigations but on this occasion a couple of factors seem to have compelled it to do so.

One was that Russia asked for its critique to be included "as an official-series document of the Ninetieth Session of the OPCW Executive Council" – in other words, made public. 

The other factor was the leaking, earlier this month, of an internal document written by OPCW employee Ian Henderson which suggested the Douma cylinders had been "manually placed" rather than dropped from the air.

The argument about "air-dropped" versus "manually placed" is an important one. If the cylinders were dropped from the air the obvious implication is the Assad regime was responsible, since rebel fighters in Syria had no aircraft. "Manually placed", on the other hand, has been claimed as evidence that rebel fighters faked a chemical attack in order to discredit the regime.

Henderson's assessment was not mentioned in the FFM's official report – prompting claims on social media that it had been suppressed for political reasons. The Working Group on Syria, Propaganda and Media – which published the leaked document – presented it as evidence that the OPCW “has been hijacked at the top by France, UK and the US”.

The OPCW's explanation is that the job of the FFM is to establish the facts about alleged chemical attacks. However, the FFM's mandate does not allow it to indicate who was responsible and there were concerns that Henderson's suggestion of "manually placed" cylinders went too far in that direction. Consequently, his report has been passed to the OPCW's newly-created Investigation and Identification Team which does have a mandate to assign responsibility for chemical attacks.

It might seem odd that the FFM's interpretation of its mandate allowed it to talk about air-dropped cylinders but not manually placed cylinders. This point is addressed in its reply to the Russian critique.

Russia says the calculations in the FFM report imply the cylinders were dropped from a height of less than 200 metres and adds: "Syrian Air Force helicopters do not fly at altitudes of less than 2,000 metres when cruising over towns, for security reasons. A helicopter flying at 200 metres over an active combat zone will come under fire from small arms at the least, and will be inevitably shot down."

The OPCW's reply makes clear that the FFM report made no mention of aircraft or the height of flight because that would be outside its mandate. It says "reverse scientific calculations" were used to determine the possible "range of force, velocities, and trajectories" for the cylinder to have caused the damage observed at the site:

"The FFM does not base its modelling or calculations on assumptions about the height from which the cylinder could have been dropped or the height of an aircraft. Therefore, in accordance with its mandate, the FFM did not comment on the possible altitudes of aircraft in any assumed operation modality."

It adds:

"The FFM report does not refer in any part to 'the argument that they were dropped from an aircraft'. Also, the FFM report does not elaborate in any part on the 'high probability that both cylinders were placed at Locations 2 and 4 manually rather than dropped from an aircraft'. In fact, this type of information is deemed outside of the mandate and methodology of the FFM. The FFM stands by its report in all aspects, including those regarding conclusions as to the use of a toxic chemical as a weapon."