The basis for our justice system stems from the notoriously pagan Vikings, who instituted trial by jury to keep vendettas from spinning out of control. Also, it borrows heavily from the jurisprudence of pagan Rome. I'm not sure which part stems from a belief in God, since OT justice consisted of "an eye for an eye and a tooth for a tooth."
Plus a massive input from English common law, which was quite distinct from the separate system of Church cannon law. We got another big input from yet another separate system -- merchant law, which arose to govern commercial conduct at the market place.