I was on I-80 in Iowa in my car with California license plates. I was going 15 over PSL with a slower car on the right lane for comparison making me very obvious for speeding. A hard to see LEO was cruising on the opposite lane and hit me with I/O Ka. I slammed on the brakes and slowed down to 5 below PSL and maintained the speed. He immediately turned around at the nearest emergency median crossover and followed me for 2 miles. He then drove to my side and we were parallel to each other for about 30 secs. I was expecting to get pulled any moment but to my surprise nothing happened. He just stepped on it and drove off. Do out of state license plates make any difference here?