the US will not allow one because it would upend its agenda:  regime change.   remember WMD in iraq?  it is highly possible the gas was manufactured by the rebels and purposely stored in the civilian populated areas and probably with the help and direction of america's covert cia group, “regime change assassins”, who may have known that an attack by syrian war planes was imminent.   when syrian war planes dropped their conventional bombs, it triggered the expected tsunami sized catastrophic (for assad) chain of ideal (for america) events by setting off the gas and killing innocent civilians and portraying the ghastly bombing aftermath on television for the world to see and insinuate that it was the syrian warplanes which were responsible for the gas.  this lie? now has developed into a life of its own and is now the truth.  and lame street media will pound it into your psych as being the truth even if evidence turns up showing the contrary.  ask yourself.  who benefits from this crime?