Law enforcement impersonation is apparently, "a thing." To the point, where police talk about the phenomenon as something they expect to see in the course of a normal career.

https://www.youtube.com/watch?v=v6nQyuP0RU4

I had my own run in with a police impersonator in Texas. I was held up very early in the morning at gunpoint by a guy who came out of a white pickup truck. I had to explain to him that I needed to take my foot off the brake and lower my hands in order to shift into park, before I could get out of the car. His story, was that he was staking out the ATM because a number of robberies were happening there.

Later on, I told the story to a musician friend of mine who happened to be a judge, and he told me that wasn't a police officer. There were absolutely no unmarked pickup trucks being used by the police.

Some impersonators apparently go to great lengths to equip themselves, even to the point of building their own fake police cars.