It's described as "The end of the security (forces) at the hands of Salman Al Farisi battalion, Free Al Bab Brigade", and the writing on the bonnet of the vehicle at the beginning of the video reads "Brigade of the Free of Al Bab and the East, Sulliman Al Farisi Battalion" and "FSA". The location of the video appears to be "Saba'a Bahrat" in Aleppo.
A post made a few minutes later claims that the Salman Al Farisi Battalion destroyed 3 tanks, and killed a bus load of army and shabiha members, in a joint operation with Al-Nusra Front. It's unclear if it's related to the above video.
The Facebook account appears to have been opened on June 10th, 2012, and has used other Youtube channels in the past, so it appears to be a genuine opposition battalion.
Thanks to @ali_alsanah, @ArarMaher, and @HasanSari7 for help with translation.
Update September 10th The Syrian Observatory for Human Rights has picked up on this and posted an additional video from the scene apparently showing members of the group responsible with the bodies
Update September 11th The New York Times has a piece on the executions which includes this
Update October 4th Now Lebanon reports Al-Nusra Front has claimed responsibility for the executions, from their statementIn one of the videos showing the executed soldiers, a narrator claims that a rebel battalion called Salman al-Farisi was responsible for killing the men. A man who claimed to be a representative of the battalion, contacted through its Facebook page, condemned the killings but said he was not sure whether members of the militia were responsible for them. The video of the executions was subsequently removed from the battalion’s Facebook page.
God enabled the mujahedeen of the Al-Nusra Front in the city of Aleppo to capture and kill 20 heretic soldiers from the Hanano military postThe image described in the Now Lebanon article appears in this article, apparently showing a member of Al-Nusra Front in the process of executing the prisoners.
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