I just watched/listened to the Obama UN speech on Sept 25, 2012. He absolutely and repeatedly refers to a root cause of the violence in Benghazi being the video slandering the prophet of islam.
He does it from the 13 minute mark through the 21 minute mark in the 30 minute speech. The key quote is at 20:36.
http://www.youtube.com/watch?v=73EQoIsKwCw