CAIRO — After a month of conflicting statements and partisan criticism, the circumstances surrounding the attack that killed Ambassador J. Christopher Stevens in Benghazi, Libya, on Sept. 11, 2012, have become clouded in ambiguities and questions: Did the attack grow out of anger against an American-made video mocking the Prophet Muhammad, or was it waged by an affiliate of Al Qaeda out to mark the 11th anniversary of its attack on United States soil?

To Libyans who witnessed the assault and know the attackers, there is little doubt what occurred: a well-known group of local Islamist militants struck without any warning or protest, and they did it in retaliation for the video. That is what the fighters said at the time, speaking emotionally of their anger at the video without mentioning Al Qaeda, Osama bin Laden or the terrorist strikes of 11 years earlier. And it is an explanation that tracks with their history as a local militant group determined to protect Libya from Western influence…

United States intelligence agencies have reserved final judgment pending a full investigation, leaving open the possibility that anger at the video might have provided an opportunity for militants who already harbored anti-American feelings. But so far the intelligence assessments appear to square largely with local accounts.