This now deleted, but archived Dailymail article spells it out fairly clearly- internal emails from a company called "Britam Defence" appear to show that the US government and Qatari government hired them to fire off a Libyan-origin but Iranian-style chemical weapon in Homs while speaking in Russian and recording it.
That this would give the west a reason to destroy Syria and blame Russia and Iran for the entire problem is of note- what may be more of note is that the article itself was apparently pulled offline and now is available only from the wayback machine archive.
Obama himself of course has said the use of chemical weapons in Syria would be crossing a line which would necessitate US intervention.
My thoughts- the USA wants to grab up Syria as a western ally to offset the possibility that Cyprus will go the way of the Russian as it appears that at the moment the Russians are/ are considering bailing out Cyprus' failing banking structure through Russian banking and business firms. Cyprus is, of course, a strategic site in the ocean, close to Syria and Israel.