Back in college, I was the house and risk manager for my fraternity. As you can imagine, this was a stressful job, as I was forced to monitor not only the many idiotic whims of my brothers, but the potential impact those ideas had on our house.
My least-fond memory of those hazy years involved a brother who drove a retired police cruiser. He desperately wanted to be a cop and took to driving his blacked-out, push-bar-equipped Ford Crown Victoria like Martin Riggs from Lethal Weapon. While his typical days were spent terrorizing other motorists by suddenly appearing in their rearview mirrors, one day he decided to lead the campus police on a high-speed chase (as one does).
He got ahead of them, hid his car and ran into the fraternity house, breathlessly telling me he'd been there the whole time. The police arrived, having ran his plates and asking for him by his last name... which happened to be the same as my first name. Shockingly, neither he nor I were arrested that day (keep in mind, these were just campus police), but I've since become a firm believer that unless you want to start a second life as a taxi driver, you should not buy a used police car.
If you choose to ignore me, though, Yahoo! Autos has put together a smartly comprehensive buying guide, written by a dealer, that details the ins and outs of the police car buying process. It ranges from what sort of equipment you should bring to a city auction, to what kind of cars will go for the least money. It's a rather interesting read and provides a glimpse into a market of automotive sales that nearly every enthusiast has thought about at least once.
Head over and take a look.