Video shows police responding to a call of an alleged domestic disturbance involving a drunk man who assaulted a juvenile

Perry Lowry, 49, is seen on the floor, face down, as two officers restrain him

One cop grabs his head and repeatedly, forcibly slams it on the ground

A terrified onlooker was heard pleading with them, telling them, 'don't kill him'

'I think he's dead,' he added after the officer finally let go of the  seemingly unconscious suspect