Obama did not present any direct evidence to back up his assertions. He said he is still evaluating options for possible military retaliation, but vowed that any American response would send a "strong signal" to Syrian President Bashar Assad.
Obama said in a PBS interview that the U.S. has concluded that the Syrian government carried out the chemical weapons attack and "there need to be international consequences."
The president says he's not seeking a lengthy, open-ended conflict in Syria, indicating that any U.S. response would be limited in scope.
http://accesswdun.com/article/2013/8/264977