Colum Lynch and Joby Warrick
The Washington Post 
June 21, 2013
Despite months of laboratory testing and scrutiny by top U.S. scientists, the Obama administration’s case for arming Syria’s rebels rests on unverifiable claims that the Syrian government used chemical weapons against its own people, according to diplomats and experts.
The United States, Britain and France have supplied the United Nations with a trove of evidence, including multiple blood, tissue and soil samples, that U.S. officials say proves that Syrian troops used the nerve agent sarin on the battlefield. But the nature of the physical evidence — as well as the secrecy over how it was collected and analyzed — has opened the administration to criticism by independent experts, who say there is no reliable way to assess its authenticity.
The technical data presented by the three Western powers is of limited value to U.N. inspectors trying to determine whether
Syria’s combatants used chemical weapons during the country’s 25-month-old conflict. Under the United Nations’ terms of reference, only evidence personally collected by its inspectors can be used to fashion a final judgment.
But no inspectors have been allowed inside Syria, so Western governments have relied on physical evidence smuggled out of the country by rebels or intelligence operatives. Precisely who acquired the evidence and what methods were used to guard against tampering may be unknowable, according to experts experienced at investigating chemical weapons claims.
Full story here.