If you were doing 56 or more in a 55 zone, your guilty, period. It does not matter if the cop was doing 100mph, he is exempt from speeding laws. If you are going to loose your drivers license because of this, you should hire a lawyer.
What he said minus the cop speeding part. Unless the car has the lights flashing he himself is violating the law. That said good luck proving it. Unless you have speed detecting equipment (i.e. Radar gun) and video evidence, it not going to happen. I believe dateline did a special on this in October of 2013.
