Elo... I'm gonna guess that you are extremely sheltered. If there were technology capable of tracking and arresting criminals, then it would have already been made. There is no way of coding any type of machine to track bad people and arrest them, if there was, police would not exist, heck, the government might not exist. There is no way to catch every single criminal in the world or even just the US. Besides that, things aren't always black and white. If there were technology capable, then who's to say that it would get it right in every circumstance? There are murderers who are only that because of self-defense. In court, if you testify self-defense and have evidence that it was, then it doesn't count as manslaughter. Besides, how would it tell that they were a criminal? Detectives have to use unreplicable brainpower just to figure out how a crime happened, who did it, and what evidence they have. There isn't a machine that can just scan you and say "Yup, you killed someone" because it's impossible to look at someone and be able to tell. Even lie detectors are faulty because some people are nervous just taking a lie detector test and some liars know how to lie right through the test without hesitation or an unsteady heartbeat.