A couple of judges in Pennsylvania plead guilty to a kickback scheme of where they got money from a privately run youth detention center company. They are accused of sending kids to this private jail in exchange for money.

http://www.nytimes.com/2009/02/13/us/13judge.html?_r=1

The article makes no mention of these types of companies also lobbying state governments for tougher (and more) laws that put more people in jail, but it also happens. The moral of the story is that if somebody can make a profit from putting people in jail, more people are going to be put in jail.  It’s probably not a good idea to let private companies into the justice system if you want anything that even resembles justice rather than a profit motive.