Hi, one way to get started is to simply make a list of all the reasons why you think the criminal justice system is fair.  As you write out your ideas, you'll begin to see certain ideas or themes repeat themselves.  Try to crystalize these ideas into one main idea or argument that will be your "thesis" (which is what you are trying to prove in your essay).

Your outline will then be a list of your key ideas, including your main idea (your thesis).  Good luck!