From what I read, it seems that the rebels are not a unified movement with the same goals, beliefs, vision for the future Syria, friends or even approaches to the conflict. The only thing that seems to unite them is removing the Assad regime. So, considering them as a united front seems like going down the wrong path when looking for their potential involvement.

There are reports that outside fighters tied to Al-Qaeda type movements are involved in anti-Assad actions. I suspect these folks do not support interests of the USA or the west.

The same goes for the other side in the conflict. Assad mostly has control of his forces, but it seems that Iran has a major influence on Hezbollah, that currently fights the rebels in support of keeping Assad in power. It is likely that both Iran and Hezbollah have broader interests than only what occurs in Syria and do not seem too warm to western countries influence in the region (especially those linked to Israel). With USA concerns over potential actions over it's nuclear program, Iran gains when another front opens for the USA and an additional wedge is placed between the USA, Russia, China and USA allies. USA looses much credibility when it uses bombbs- at home and abroad.

Many previous USA military involvements in other countries have been conducted with much PR to get the public (USA and potential allies) and political support. This one was different, as the Obama team seemed unprepared and faced an uphill battle. That leads me to believe that the administration was not involved. It is possible that rogue elements within the USA government was involved, but they seem more under control of the government in power than the past.

It is just as feasible that rogue elements within the Assad regime (for example the military)were involved, but unlikely that the regime would not know, or at some point know about it (considering the control he seems to have). Getting the USA mired in another unwinnable conflict could be a goal- especially when Russia is on your team as a friend. Sending a warning message (that chemicals are in your arsenal) to the rebels is another potential reason to use them in a small test situation.

There are plenty of potential groups among the potential that have little concern for civilian causalities in obtaining a broader goal. Additionally, all Syrians are not friends, civilians or otherwise.

I don't know who did it- just letting my mind wander a bit over potential candidates and potential reasons they may (or may not) have..