Simple
Just like each player has 3 (primary) skills, and they own a car under their client (keep in mind the GUI we discussed today) my reasoning is you can pay $x as an up-front fee and $x each day/week/month to keep the lawyer. The lowest tier lawyer is supplied for you, free of charge, by the state. You have a 5% chance of lowered charged. The lowest tier purchased lawyer is 10%, all the way up to 45% deduction possibility
This means there's no need for a judge, jury or lawyer, while still having the functionality of one: bob might go to jail for 3 years, but because john had a great lawyer he only gets 9 months
I have no idea how much lower the charges should go though. I just think it would be neat to be able to get out of a crime for less, especially if you're going to go into a criminal lifestyle, like robbing and car jacking