Here's why the U.S. is so sure that Syrian president Bashar al-Assad's government was behind a deadly chemical attack on August 21: U.S. intelligence listened in on a phone call between a Syrian Ministry of Defense official and someone at the country's chemical defense unit. That call, according to a report at Foreign Policy, is more or less why the U.S. is certain that Assad's government bears responsibility for the massacre near Damascus.
Based on the evidence, the U.S. is all but certain to take some course of limited military retaliation against the Syrian army for the chemical attacks carried out in Syria. While President Obama is still officially considering his options, there's little evidence to suggest that the U.S. will continue to stick solely to a diplomatic approach towards the country.
Previous reports have indicated that the U.S. was relying in part on intercepted communications relating to the chemical attack in their assessment. According to CNN, an intelligence report on Syria, planned for public release in the coming days, will include intercepted intelligence along with forensic information. That report is being compiled by the Office of the Director of National Intelligence, and could be released by Thursday. Rumors of an intercepted phone call were picked up widely by the conservative press for days after the German magazine Focus spoke to an anonymous Israeli intelligence official, who claims that the intercepted phone call comes from intelligence gathered by one of their elite units. Foreign Policy, however, specifies that U.S. intelligence overheard the call.