If Syrian government forces did not launch the chemical attacks near Damascus on August 21, we have to assume that rebel fighters did. Short of denying that the attacks took place at all, there is really no other possibility.

Although many people continue to dispute that the Assad regime was responsible, no one has yet come up with a plausible theory – let alone hard evidence – as to how the rebels might have done it.

The chemicals

We know the Syrian regime had plenty of Sarin as well as the type of rockets that were almost certainly used to deliver it in the August 21 attacks. In order to make a persuasive case that blames the rebels it would therefore be necessary to show that they too had access to Sarin in large enough quantities, as well as the relevant munitions.

As far as rebel Sarin is concerned there are three possibilities:

1. It was obtained from outside Syria
2. Rebels produced it themselves
3. It was stolen/captured from the Syrian regime's stockpile

The third possibility can be eliminated immediately because the regime has insisted throughout the conflict that its chemical weapons are secure and it has not reported any losses.

To advance an argument that Sarin came from outside Syria it would be necessary to identify possible suppliers: who was in a position to supply, and could they realistically have done so?

If the rebels made their own Sarin – a complex and dangerous process in itself – who did they manage to do so without detection and, apparently, without mishap? One might reasonably expect Syrian intelligence to have been on the lookout for this and eager to publicise any incriminating evidence they found. But apart from vague claims about chemical "factories" they have come up with nothing that clearly points to Sarin production by rebels.

The munitions

According to the Syrian regime, rebel fighters have used small quantities of Sarin on several occasions. One of these, allegedly, was in Khan al-Asal last March. The facts are disputed but the regime's version (cited in the latest report from UN weapons inspectors) is that rebels fired a chemical rocket from 5km away. 

If this were true (and it may not be), the rocket cannot have been of the same type that was implicated in the August 21 attacks, since their probable range has now been established at a little more than 2km.

In the days following the August 21 attacks, the regime also accused rebels of attacking its soldiers on three occasions with canisters that emitted gas. The UN inspectors were unable to confirm this but, even if we accept the regime's version, the point to note is that the munitions allegedly used were fairly small. One is said to have had a capacity of four litres and one is said to have been launched from a catapult.

If we take the regime's claims at face value that still doesn't go very far towards convicting rebel fighters for the August 21 attacks. If we assume the rebels did use Sarin in these other incidents there's nothing to indicate they had enough of it for August 21, when it appears that hundreds of litres were used.

Also, the regime's claims about other usage of "rebel Sarin" do not link the rebels to the type of munitions implicated in the August 21 attacks.

In their report on the events of August 21, the UN inspectors stated:

• "Impacted and exploded surface-to-surface rockets, capable to carry a chemical payload, were found to contain Sarin."

• "Close to the rocket impact sites, in the area where patients were affected, the environment was found to be contaminated by Sarin."

The rockets concerned were of a type which is so far unknown outside Syria and which is known from video evidence to be used by the regime. There is no evidence, at least so far, of them being used by rebels.

To make a persuasive case against the rebels, therefore, it would be necessary to show how they could have acquired them, along with suitable launchers. Could they have captured them from regime forces? If that were what actually happened, why hasn't the regime said so?
   
Posted by Brian Whitaker
Monday, 16 December 2013