That's an interesting question, I've never really considered what the criminal justice system of the future will be like.
My assumption is that, with the advancement of technology, espionage, data mining and surveillance - it will be increasingly more difficult for people to commit crimes and get away with it in the real world.
Perhaps advanced bionics will be able to predict the frame of mind a person is in based on biological signals and this, paired with an advanced algorithm, will be able to alert law enforcement to situations where someone is at 'high risk' of committing a criminal offence (Minority Report anyone?)
The other thing I'd like to think would change about a criminal justice system in the future is the way people are punished:
I hope prisons where offenders go in only to emerge after their sentence even more criminally minded and marginalized changes.
Instead, perhaps as a society we could think up a punishment that is bad enough to act as a deterrent, but which will actually teach prisoners a skill that they could use once they get out. And maybe their time in prison could also be used doing something constructive that will pay back society.
What exactly? Well, the society of the future will be heavily dependant on technology, and all that software will need debugging.
What could be more painful than years on end of debugging code?