The murder video appears to have been shot with 2 cameras (with different time stamps).
Was Nick Berg castrated/genitally mutilated? If so, that could account for the screams you hear before his neck has been cut.
The long version, almost 10 minutes, has the screaming while the camera shows him still looking at the camera, and the shouts of Allhu Akbar begin, but Berg is NOT the one screaming. He just sits there motionless. Sitting upright.