Something to consider, most, if not all, police motors that are sold either at auction, or private sale, besides having alot of wear on critical parts such as alternators, and wiring harness, brakes and suspension, will all have one thing in common....
Most departments do not have motorcycle trained mechanics and are simply serviced by the motor pool mechanic who repairs their cars and SUV's, this may or may not be a concern, however, one important thing to consider is when they take the motors out of service, someone simply takes a pair of side cutters and chops off all the lights/horns/sirens/and accessories, often leaving the wire harness open/damaged/exposed. Before you pull the trigger on a police motor (pun intended) I would completely check the unit over from one end to the other, checking for bent or damaged rims/forks/steering stems (jumping curbs) brakes (often neglected) and condition of the main wire harness etc.
As others have pointed out, you can get a much nicer civilian model with ABS and less miles for the same or lower price. Its a buyers market out there right now for ST's.