Originally Posted by mineistaken

You can identify even with some common sense. I mean it won't be 100% accurate, but still. Like you identified those people from your school that you knew were going to be criminals.
On top of that common sense you add some theory, statistics and so on and you can make good assumptions which people have high chances to be life time criminals, which people have high chances to be decent citizen and so on. Again, it would not be 100% accurate, but at least much better than putting all of them in one pot and treating exactly the same.