LATimes: "US Intel confident poison gas was released but are less sure about whether Bashar Assad's regime is responsible!"

"WASHINGTON — U.S. intelligence agencies unanimously agree that Syrians have been exposed to deadly sarin gas in recent weeks, but they are divided over how certain they can be that the Syrian regime is to blame, U.S. and congressional officials said Friday.... 
Gary Samore, who was the White House's top official on weapons of mass destruction until February, said that answering questions about the "chain of custody" would probably depend on highly sensitive intelligence that might not exist, or which the government would be reluctant to make public.
As a result, "I think there's always going to be doubt," said Samore, now with the Belfer Center at Harvard University....
If the U.N. team continues to be blocked, the administration will have to rely on its own intelligence assessments and that of allies, which would not be nearly as convincing to the rest of the world. Greg Thielmann, a former U.S. intelligence analyst, said the intelligence agencies' conclusions would probably be less convincing to the public because the agencies are not likely to declare that they have reached 100% certainty.
"The Iraq WMD is looming over this, as it ought to be," a senior congressional official said. "How can you be more confident in the assessment here? These are questions we are all asking." ..."