A series of revelations about the rocket believed to have delivered poison sarin gas to a Damascus suburb last summer are challenging American intelligence assumptions that government forces carried out the attack.
The conclusions of a team of security and arms experts suggest that the case US officials initially made for retaliatory military action was flawed.
The experts, meeting this week in Washington to discuss the matter, have concluded that the range of the rocket that delivered sarin in the largest attack that night was too short for the device to have been fired from the Syrian government positions where the Obama administration insists they originated.
Separately, international weapons experts are puzzling over why the rocket in question, an improvised 330mm to 350mm rocket equipped with a large receptacle on its nose to hold chemicals, reportedly did not appear in the Syrian government's declaration of its arsenal to the Organisation for the Prohibition of Chemical Weapons and apparently was not uncovered by OPCW inspectors who believe they have destroyed Syria's ability to deliver a chemical attack.
Neither development proves decisively that Syrian government forces did not fire the chemicals that killed hundreds of Syrians on the morning of August 21. US officials continue to insist that the case for Syrian government responsibility for the attack in East Ghouta is stronger than any suggestion of rebel involvement, while experts say it is possible Syria left the rockets out of its chemical weapons declaration simply to make certain it could not be tied to the attack.
"That failure to declare can mean different things," said Ralf Trapp, an original member of the Organisation for the Prohibition of Chemical Weapons and a former secretary of the group's scientific advisory board. "It can mean the Syrian government doesn't have them, or that they are hiding them."
In Washington, the Office of the Director of National Intelligence said its assertion of Syrian government responsibility remained unchanged.
"The body of information used to make the assessment regarding the August 21 attack included intelligence pertaining to the regime's preparations for this attack and its means of delivery, multiple streams of intelligence about the attack itself and its effect, our post-attack observations, and the differences between the capabilities of the regime and the opposition. That assessment made clear that the opposition had not used chemical weapons in Syria," it said on Wednesday in an e-mail.
The authors of a report released on Wednesday said that their study of the rocket's design, its likely payload and its possible trajectories showed that it would have been impossible for the rocket to have been fired from inside areas controlled by the government of Syrian President Bashar al-Assad.
Meanwhile Italy said the southern port of Gioia Tauro will be the site for the transfer to a US ship of chemical weapons materials from Syria. The first load of materials for poison gas and nerve agents are aboard a Danish ship, and Italy has agreed to serve as the transfer port to the US cargo vessel Cape Ray for eventual destruction at sea.