In 1998, the author spent a year following the events in one courtroom in the Chicago courthouse that deals with criminal cases. The book was published several years later, and consequently the author has some information about what happened to the judge and some of the defendents.
There are tens of thousands of cases that come through the courthouse every year. The Cook County Jail, attached to the courthouse, does not have anything like the space to house all of the defendents. Most of these cases are low-level drug cases. Consequently, one aspect of the judge's work is to dispose of cases quickly. Almost all cases are disposed of in plea bargains between the prosecutor and typically a lawyer from the public defendent's office.
A large majority of the defendents are black, with a sprinkling of Hispanics and fewer whites; almost all the judges, prosecutors and public defendents, and jurors are white.
One thing I learned is that you invoke your right to a trial, particularly a jury trial, only at your peril. You better have a good case, because if you lose you will end up doing more prison time than if you had taken the plea bargain. Although Illinois does not (at the time anyway, don't know whats happen since) have mandatory minimum sentences for drug cases, as the federal and some other states do, the system still pushes people to plead guilty to what the prosecutors offer. As the prosecutors may offer time served or probabition rather than prison time, people who are innocent will plead guilty to felony in order to avoid the possibility of prison time, or to reduce their prison time.
A great deal of lying goes on in the courtroom when a case comes to trial. The defendents often lie, the police lie (to read police reports, there are an astounding number of people who happen to drop their illegal drugs onto the sidewalk when a police officer happens by), and it can be in the tactical interests of both prosecutor and defense lawyer to avoid bringing up in court what may have actually happened. Cases appear to turn almost entirely on eyewitness testimony.