Jody McIntyre (@jodymcintyre) is a young man in a wheelchair. He tells his story at his blog, which you can find here. The most salient information comes here:

From the corner of my eye, I spotted one of the policemen from the earlier incident. He recognised me immediately. Officer KF936 came charging towards me. Tipping the wheelchair to the side, he pushed me onto the concrete, before grabbing my arms and dragging me across the road.

Can any more information be shed on Officer KF936? Huge credit to Jody for telling his story so passionately and with clarity on his blog.