You can hear what sounds like open faucets. It's the sound of blood gushing from the head wounds.
The video clip lasts a mere 35 seconds. It's night. Six men, illuminated by a flashlight, are sitting with their hands tied behind their backs and with various types of blindfolds.
More men huddle behind them in the dark. In front of them is a pit, apparently freshly dug, and on the other side of the pit sits another man similarly bound and blindfolded.
Two seconds into the clip, someone says, "Jahiz?" "Ready?"
At three seconds a man extends his right arm into the light, holding a pistol.
At six seconds the first shot is fired into the back of the first man's head. The man with the pistol moves decisively, without hesitation, shooting one after the other in the back of the head. It would appear he has done this before many times.
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Eleven seconds into the video clip, you can hear what sounds like open faucets. It's the sound of blood gushing from the head wounds. And the gushing sound gets louder and louder.
Twenty-six seconds after the first shot is fired, a total of 14 men -- some of whom appear to be teenagers -- are dead or dying, some slumping into the pit.
This video clip was one of a variety recently obtained by CNN from Syrian activists. They document atrocities committed not by the regime of President Bashar al-Assad, but rather by members of the Islamic State in Iraq and Syria, known as ISIS, which emerged last year as a major power in opposition-controlled parts of northern Syria.