Mark LeVine is professor of Middle Eastern history at UC Irvine, and distinguished visiting professor at the Center for Middle Eastern Studies at Lund University in Sweden. He often writes analytical opinion pieces for Al Jazeera. His position is perhaps a good place to start
"It is simply not conceivable that the US, Israel, Saudi Arabia or other major players would allow any of the Sunni jihadi groups operating in Syria to build up a significant stockpile of chemical weapons and use them on numerous targets simultaneously. The risk that these weapons could be used against Israel, the US or other targets would be too great to allow. "
Notice the strength of LeVine's conviction. The scenario is not just improbable. It is inconceivable. Note also his high opinion of the ability of US, Israel, and Saudi Arabia to ensure militants do not stockpile enough chemical weapons to carry out the Damascus attack. Yet the Damascus attack was really not as huge as it first was hyped as. Not only that the quality of the chemicals used seem to have been less than military grade. Otherwise as experts have noted, rescue personnel and doctors could not have treated the victims without protective gear or they would themselves be victims.
Lost in all the discussion of the issue is evidence
that the rebels do have access to chemical weapons, in particular sarin gas:
Turkish security forces found a 2kg cylinder with sarin gas after searching the homes of Syrian militants from the Al-Qaeda linked Al-Nusra Front who were previously detained, Turkish media reports. The gas was reportedly going to be used in a bomb.
NOTE: The Syrian ambassador in his speech says "two liters" not kg. I don't know which is correct.
Some rebels have actually boasted
of their capacity to launch chemical weapons attacks. Political adviser of the Free Syrian Army Bassam Al-Dada said that the Army had all the components to produce chemical weapons and knew how to put them together and use them if necessary. He stressed that they would only use them if the Assad regime used them first. Speaking to the Turkish Anatolia news agency he said that Assad should know that if he uses chemical weapons the opposition also has them.
There is also considerable evidence that the rebels used chemical weapons in the Khan al-Assal area of rural Aleppo in March. The Syrian government asked the UN to investigate but then the rebels demanded that there be investigation of a number of other incidents as well. However, the investigation of this incident was one of the tasks of the present group of inspectors. I expect that they will probably never get to the site. Russian experts were able to investigate the site and concluded that the attack was by the rebels and used sarin gas. As the Syrian Ambassador to Syria mentions in his speech the Russians had given extensive documentation to the UN about their investigation but nothing has ever been heard since. Right from the start the UN refused to carry out any investigation that would assess who was responsible for the attack. Rebels with the support of the west then also demanded an investigation of a whole series of other alleged chemical attacks.
About the Khan al-Assai incident, Carla del Ponte, a UN investigator said in early May:
Testimony from victims strongly suggests it was the rebels, not the Syrian government, that used Sarin nerve gas during a recent incident in the revolution-wracked nation, a senior U.N. diplomat said Monday.
Carla del Ponte, a member of the U.N. Independent International Commission of Inquiry on Syria, told Swiss TV there were “strong, concrete suspicions but not yet incontrovertible proof,” that rebels seeking to oust Syrian strongman Bashar al-Assad had used the nerve agent.
The Syrian government is demanding
that the UN investigate immediately what they allege are three more chemical attacks carried out by rebel groups just outside of Damascus. I expect this is unlikely to happen because of security concerns. They might be hit by incoming missiles. I hope I am wrong and this is not conceivable.