Your on your way home alone from work/function/etc in the city. You are equipped with your normal EDC. It is around 2330 on a Wednesday night and traffic is very light. The road is a typical four lane boulevard with a left turn lane in the center. Up ahead you see a marked patrol car stopped on the right side of the road with its emergency lights on and another vehicle in front of it in what appears to be a traffic stop.
As you draw near, you see a uniformed officer on the ground on his back. His feet are toward you on the grass parkway and his upper body is on the sidewalk. There is a large male atop the officer pummeling him. Adjacent to the sidewalk is a large grass area fronting some sort of business building about thirty yards back that is all dark. As you slow you see the officer trying to ward off blows with his arms as the male continues to pummel him.
You stop and as you exit your vehicle, you hear no sirens or fast approaching vehicles and see no other vehicles in sight. As you round the front of your vehicle, you are about ten feet from the male and the officer. Neither the officer or the male atop the officer, who has his back to you, shows any awareness of your presence and he continues to pummel the officer whose resistance appears to be weakening.
What do you do?