Syria: a hell we can't solve.
The question does remain though as to what was used, and who deployed it. It could be sarin that has degraded, or some other form of organophosphate that has been weaponised. The other quandary is how it was deployed: Brown Moses has videos showing what seem to be Syrian-manufactured munitions, the same as those found in proximity to previous alleged chemical weapon attack sites. This in itself doesn't really help us as to who fired them: while the rebels have relied on jerry-rigged and amateur weapons systems, we don't know whether the regime had systems capable of delivering chemical weapons at the outset of the rebellion, and so they may well have had to improvise themselves.
Most perplexing is why the government would have chosen to carry out the heaviest attack of the war just as the UN weapons inspectors have been allowed in, and indeed, are apparently only 6 miles away from ground zero. It could be that this is Assad emphasising his position of strength, convinced that he now has the upper hand in the conflict and so prepared to show the complete impotence of the international community. Conversely, it could be the rogue commander issue again, or that in this instance the chemical hadn't degraded as much was expected, or that more was used than was authorised. If, on the other hand, this was an attempt by the rebels to frame the regime, did they make the same mistakes as the Syrian military may have done, not expecting there would be so many apparent casualties?
On the balance of probabilities you'd have to say that the simplest explanation, that this was a chemical attack by the government, authorised at the highest levels or not, is also the best one. If this truly wasn't the actions of the regime, then there shouldn't be a problem with allowing the UN inspectors to visit the site, especially as they would quickly be able to conclude whether this was a sarin attack or the use of some other sort of chemical.
Sadly, such has been the bloodshed in Syria that even though this marks an escalation in the type of weapons deployed, it doesn't really change anything on the ground. This is still a proxy war that we have refused to stay out of, lecturing and continuously turning up the rhetoric while not being prepared to push without conditions for a peace settlement. Instead, we've backed rebels that have committed atrocities of their own, unconcerned at the possibility the weapons we supply to the "moderates" will almost certainly end up in the hands of those who execute children and priests in cold blood (extremely graphic). The language used by politicians against Assad over the past day has also been in stark contrast to that deployed against the military in Egypt, where similar numbers have been slaughtered the past month. We've gone past the point at which we could have done something, had we wanted to; now all we can do is mouth platitudes and empty threats as two depraved, desperate sides battle against each other, with the innocent trapped in the middle.