accuracy of radar if behind two other vehicals

I was going home yesterday traveling on the same country road I've used for the last 25 years. I didn't see the patrol car coming toward me (in the other lane of course) because he was traveling behind two other cars. When his light came on I instinctively looked at my speed odometer: I was doing just under the 55mph speed limit. He passed me, turned around and pulled me, claiming he had a lock on me going 68mph. I call BS! Is it possible for radar to be 100% accurate if the trooper is 'shooting' from behind two other vehicles?

Yes, it is possible to be accurate fro behind 2 cars. The percentage of accuracy depends on many factors. Were you and/or the officer driving uphill, downhill, or around a curve? This could affect the accuracy. If the patrol car was far enough behind the vehicle in front of them (distance would depend on the radar gun) it can still be extremely accurate. Most modern law enforcement radar guns can be set to ignore one direction of traffic (traffic going the same direction in your example) and only read the oncoming traffic.

Check out the book, Traffic Radar Handbook: A Comprehensive Guide to Speed Measuring Systems. This may give you some useful information.