The Guardian tries to be coy with this August 27 article (April & August attacks, but the conclusion is clear: UN thinks that the Insurgents did it!
"As the Syrian revolt continues to tear the country apart, the international community has been eager to condemn Syrian President Bashar al-Assad, even as it became clear that the rebels do not, in fact, represent a popular uprising against the oppression of the Assad regime. According to UN diplomat Carla del Ponte, however, it appears that the recent chemical weapons attack, in April (READ the UPDATE below on August 21st attack) , was carried out by the Syrian rebels and not the regime, as it had been widely assumed. Speaking to a Swiss television channel, del Ponte said that there were “strong, concrete suspicions but not yet incontrovertible proof,” that rebels had carried out the attack. She also said UN investigators had seen no evidence of the Syrian army using chemical weapons,
UPDATE: This article was updated to clarify one or two points that some of our readers found misleading: The chemical attack earlier this year was widely blamed on the Syrian regime. It is this attack that the UN now concludes was carried out by Syrian rebels. It appears unlikely – for a number of reasons – that the most recent August 21st attack was carried out by government forces – despite the rush to judgement within the international community – although this has yet to be fully determined. It is clear that both sides in the Syrian conflict have the means to use chemical weapons and it would be misguided to assume that either side has a moral objection to such attacks. As Jean Pascal Zanders, formerly of the European Union Institute for Security Studies, has pointed out ”In fact, we – the public – know very little beyond the observation of outward symptoms of asphyxiation and possible exposure to neurotoxicants, despite the mass of images and film footage. For the West’s credibility, I think that governments should await the results of the U.N. investigation.”..."