If not in pursuit or actively trying to get to a crime scene etc...a cop has NO reason to be above the speed limit. In fact, they should be below it, and observing their surroundings and looking for suspicious activity etc...
They go at least 15-20mph over in residential/metro area roads around here most of the time, and troopers on the highway regularly speed like crazy. In fact, I was tailgated probably 1-2 feet from my rear bumper a number of times last summer while passing trucks at night going about 73-75mph (already technically 3-5 over) Who was the person 1-2 feet off my bumper? A STATE POLICE OFFICER. Who promptly opened the flood gates and went past me at great speed when I moved over. Lights on? No. Siren? No. Just speeding because they can! I should have slammed on my brakes.

Then there's the other kind of cop, the predator. They tailgate you through rich residential areas and creep you out. Or pull you over and say "your exhaust is too loud, you might wake our sleeping millionaires"

Meanwhile someone is being murdered in a bad area where there's not a cop to be found.
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