Opposition forces in Syria (Liwa al-Islam) carried out the chemical attack.
Question
Who carried out the chemical attack in Ghouta on August 21, 2013?
01 Oct, 2020Answer
Background
On August 21, 2013, rockets with chemical payloads landed around the neighborhood of Zamalka, located in Ghouta (an agricultural area outside of Damascus), resulting in hundreds of civilian casualties. A UN team visited the area and confirmed that the rockets carried sarin, a deadly nerve agent used as a chemical weapon.
There was initial skepticism that the Syrian government would have ordered such an attack, risking retaliation by the US. But information published by the US, UN, and Human Rights Watch during the following weeks convinced Western public opinion that the Syrian government was indeed responsible. This information included:
- Proof that the
volcano rockets found in Zamalka were locally manufactured by the government. - Rocket trajectories reported by the UN that were shown to intersect at a Syrian army base.
- Detection of sarin, which was known to be held by the Syrian government.
- Reports by the US government that the rockets had been launched from government territory.
- Finally, Syria’s agreement to dismantle their chemical weapons program was further seen as an admission of guilt. At that point the issue mostly disappeared from public discourse.
However, over time, some of this evidence has been found to be unreliable, while new evidence has surfaced that seems to better support the hypothesis that opposition forces were behind the attack. These include:
- Analysis of the rocket’s range showing that it could not have been launched from the army base initially suspected as the origin.
- Errors in the UN trajectory calculations that, together with the new rocket range calculation, point to a launch from opposition territory.
- Evidence of multiple instances in which the opposition used sarin or tried to acquire it.
- Videos apparently showing an opposition group (
Liwa al-Islam ) launching chemical rockets, which match the time and location of the attack on Ghouta.
This attack, and others that followed, are the subject of heated international debate, which significantly increased the risk of a US-Russian military conflict on at least three occasions. The world clearly needs an unbiased analysis of this case using advanced inference tools.
Update: In June 2021, the videos of the event were corroborated as authentic. They were matched to a field within opposition controlled territory, and that field has been shown to be in the intersection of seven trajectories calculated from images of the impact sites. See additional evidence.
We now consider this issue closed, and no longer see a need for a probabilistic analysis, as the new discoveries are clear enough to understand using standard human reasoning. We're leaving the analysis here for reference, and recording our original estimate: 87% Opposition, 13% Syrian army.
Note: While we don’t expect anyone to apply at this point, the Rootclaim $100,000 debate challenge is still available for this issue. Read more here.
Hypotheses Considered
Calculated Results
Calculated Results
1
96.4%
Opposition forces in Syria (Liwa al-Islam) carried out the chemical attack.
96.4%
2
3.6%
The Syrian army carried out the chemical attack.
3.6%
Starting Point
Initial Probabilities
Name
Initial Likelihoods
Syrian army
67%
Opposition
33%
The few prior instances of chemical attacks against civilian targets contain factors that make them poor comparisons to the attack in Syria, leaving motivation as the primary factor. An analysis of the motivating factors behind such an attack results in the Syrian army being twice as likely to launch such an attack compared to an Opposition group, i.e. 67%-33%.
Name
Initial Likelihoods
Syrian army
67%
Opposition
33%
Evidence
Effect
Sarin
Name
Effect
Updated Likelihoods
The attack was carried out using a large amount of sarin, which was known to be contained in the Syrian army’s stockpile. There are indications that the sarin contained the chemical hexamine, which was declared by Syria as being part of its chemical weapons program.
On the other hand, opposition forces were trying to obtain chemicals in order to produce sarin, and they released videos threatening chemical attacks. They could have stolen the sarin from the Syrian army, which would explain why it contained hexamine, or could have manufactured sarin themselves using a similar process. Although no opposition stockpiles of sarin were found, Syrian army soldiers were attacked by sarin multiple times, including in the days following the attack on Ghouta, meaning that opposition forces probably had access to sarin at that time.
Name
Effect
Updated Likelihoods
Volcano rockets
Name
Effect
Updated Likelihoods
The sarin was delivered via volcano rockets, which were produced and used by the Syrian army. However, opposition forces could have stolen those rockets from the Syrian army along with other munitions they acquired. Additionally, while the Syrian army carried out previous conventional attacks using volcano rockets, they were not declared as part of the Syrian chemical weapons program and are inferior to other rocket options available.
Name
Effect
Updated Likelihoods
Purported video of the event
Name
Effect
Updated Likelihoods
Videos of Liwa al-Islam fighters wearing chemical protection gear while firing volcano rockets and artillery shells in the Ghouta area were allegedly taped the night of the chemical attack. Multiple aspects of the video are uncharacteristic of a fabrication, such as it containing many irrelevant details, requiring a thorough analysis to understand its contents, and not having any slip-ups.
Name
Effect
Updated Likelihoods
Launch location
Name
Effect
Updated Likelihoods
Based on the range of the rockets, the location that they struck, and the impact direction upon landing, the launch location was a small field in Qaboun (33.5325°, 36.3412°), 2 km northwest of the impact sites in Zamalka, in an area that was opposition controlled but still close to positions of the Syrian army. Additionally, the terrain matches the features in the purported video of the rocket launch.
Name
Effect
Updated Likelihoods
Lack of intelligence reports
Name
Effect
Updated Likelihoods
Western governments have claimed that the intelligence points to the Syrian army. However, no reliable evidence was shared pointing to either side. This lowers the likelihood that the attacks were carried out by the Syrian army, which was monitored more closely than the many different factions of opposition forces.
Name
Effect
Updated Likelihoods
Moadamiyah
Name
Effect
Updated Likelihoods
The same night as the Ghouta attack, there was a reported chemical attack in Moadamiyah, on the other side of Damascus. This would imply a much larger scale of attack, which is more likely for an army attack. However, there is little evidence to support this claim, and it seems mostly based on confusion. Overall, this does not affect the analysis.
Name
Effect
Updated Likelihoods
Discussion