The idea of a computer deciding whether someone is guilty or not is a scary prospect. This is a bandwagon I'm not so sure the government should be so eager to jump on.
We have a law to make humans work exactly the same way. Law is a set of rules that say who is guilty and who's not. Only that humans are bad at being objective: http://blogs.discovermagazine.com/notrocketscience/2011/04/1...
As long as humans write the law, and that there is the notion of a sovereign people, human judges should decide how to interpret and apply the law.
I think we should strive for well written laws that don't require so much interpretation.
http://www.scientificamerican.com/article/lunchtime-leniency...