The intelligence linking Syrian President Bashar al-Assad or his inner circle to an alleged chemical weapons attack last week that killed at least 100 people is no sure thing.
Questions remain about who controls some of Syria's chemical weapons stores and about whether Assad ordered the strike, US intelligence officials say.
US President Barack Obama declared on Wednesday that the Syrian government was responsible, while laying the groundwork for an expected US military strike. "We have concluded that the Syrian government in fact carried these out," Obama said in an interview with PBS. "And if that's so, then there need to be international consequences."
However, multiple US officials used the phrase "not a slam dunk" to describe the intelligence picture. That was a reference to then-CIA director George Tenet's insistence in 2002 that US intelligence showing Iraq had weapons of mass destruction was a "slam dunk". That intelligence turned out to be wrong.
A report by the Office of the Director for National Intelligence builds a case that Assad's forces are most likely responsible for the August 21 chemical attack, while outlining gaps in the US intelligence picture.
A three-page report released on Thursday by the British government said there was "a limited but growing body of intelligence" blaming the Syrian government for the attacks. And though the British were not sure why Assad would have carried out such an attack, the report said there was "no credible intelligence" that the rebels had obtained or used chemical weapons.
The complicated intelligence picture raises questions about the White House's approach to the attack on a rebel-held Damascus suburb.
Intelligence officials say they could not pinpoint the exact locations of Assad's supplies of chemical weapons, and Assad could have moved them in recent days. That lack of certainty means a possible series of US cruise missile strikes aimed at crippling Assad's military infrastructure could hit newly hidden supplies of chemical weapons.
Over the past six months, with shifting front lines in the 21/2-year-old civil war and sketchy intelligence coming out of Syria, US and allied spies have lost track of who controls some of the country's chemical weapons supplies, according to one senior US intelligence official and three other US officials briefed on the intelligence shared by the White House.
All spoke on condition of anonymity because they were not authorised to discuss the Syrian issue publicly.