How That Neck Got Snapped

Having done my due diligence and waited for more info to come out of Philly before commenting, I'm going to link to this piece from Counterpunch (they can post decent stuff when they want to) by Dave Lindorff:

Here in Philadelphia, Police have long enjoyed giving arrested men who mouth off to them during arrests what is known fondly in the department as a “nickel ride.” That’s where they put the prisoner in the back of the van, hands bound behind their backs so they cannot hold on to anything or protect themselves, and otherwise unrestrained. Then the driver of the vehicle accelerates repeatedly, whips around corners and periodically slams on the breaks, causing the helpless captive in the back to slam against various parts of the vehicle, often with his head

Prior to reading this I was under the impression that we had a situation where a knee was put to the back of Grey in a fashion similar to what was done to Eric Garner. The above suggests strongly that it was that van ride.