The United States intelligence community does not believe the core of al Qaeda was behind this week's attack on the U.S. Consulate in Benghazi, Libya, a U.S. intelligence official told CNN Thursday. The official said the picture is becoming clearer within the intelligence community as to what group or groups were responsible for the attack. Given what officials know about al Qaeda in Libya, U.S. intelligence believes it is very unlikely that core al Qaeda was behind the attack. But the official said the intelligence does not rule out that the attack was perpetrated by al Qaeda sympathizers.