People are very predictable if you know enough about them. http://en.wikipedia.org/wiki/Correlates_of_crime Criminality is essentially a combination of low dopamine, low serotonin and low adrenaline levels. Stress chemicals such as cortisol can rapidly deplete neurotransmitter levels. There is also an inverse correlation between socioeconomic status and criminality. Being poor means more stress and lower levels of those neurotransmitters.

The impulsivity caused by dopamine deficiency also causes more unwanted pregnancies - another risk factor for criminality.

Poor people are also more likely to be religious - http://www.gallup.com/poll/116449/religion-provides-emotiona... and being religious is correlated with criminality.

So there is clearly a strong correlation between the effects of being poor or in poverty and criminality. Since the law is specifically designed to 'deal' with criminality, it is a mechanism which is quite biased against the poor. Hence, the law is there to protect the rich from the poor.