OK let's play "just suppose".
Just suppose it is true, as Assad, the Russians and many independent observers claim, that the "rebels" in Syria have chemical weapons, and that, as the chief UN inspector said in May, they have probably already used them against a civilian population.
And just suppose that it was the rebels, or someone working with or for them, that in fact used chemical weapons in August to frame the Assad government.
Then we can expect that the Assad government will strongly insist on international guarantees of protection from any further chemical weapons use by their enemies.
Given the recent history of open US support for the anti-Assad side of the civil war, that guarantor would have to be some power or combination that was not allied with the US, yet with the military heft and the will to act against the rebels if they should use chemical weapons again.
That could be a problem. The countries that first come to mind which could do this, Russia and China, have been defined as enemies or proto-enemies by the US government. With good will, the problem could be solved. Brazilian peacekeepers for example.
But I would look for those parties to the negotiations who never wanted a peaceful solution in the first place to ridicule Syria's demands for guarantees and characterize them as proof that Syria is not serious.
This proposal has to be tried. It's the best one yet, and with enough determination and patience by all parties that don't want a wider war it could defuse the situation. But the issue of who really was guilty of those chemical attacks needs to be addressed, because it shapes how we think about what can be expected of whom, and it will shape what we will see as the different parties' legitimate interests and concerns.