My best guess is that they look for anyone who is on their radar, to include people wanted for questioning in open cases, suspects in various crimes, people with outstanding warrants, and (big money maker) expired license plates. Yes, the scanners on police vehicles can glean all that info from a plate and compare it in seconds to a database of wanted people. It's relatively cheap, passive, and just another pair of "eyes" on the road. So say you're driving a friend's car, and get pulled over because your friend is wanted or has a warrant out. You'll get detained and have to identify yourself, but if you're not the person of interest, you may have to walk home... the car might get impounded, and you will most CERTAINLY be asked where your friend is at that moment.... because they really want HIM, not you.
My best guess is that they look for anyone who is on their radar, to include people wanted for questioning in open cases, suspects in various crimes, people with outstanding warrants, and (big money maker) expired license plates. Yes, the scanners on police vehicles can glean all that info from a plate and compare it in seconds to a database of wanted people. It's relatively cheap, passive, and just another pair of "eyes" on the road. So say you're driving a friend's car, and get pulled over because your friend is wanted or has a warrant out. You'll get detained and have to identify yourself, but if you're not the person of interest, you may have to walk home... the car might get impounded, and you will most CERTAINLY be asked where your friend is at that moment.... because they really want HIM, not you.