This is good question. A good closing statement should have several essential elements.
First, a great closing statement should summarize all the major arguments. This is important, because in a long trial, people tend to forget. So, when you end with a summary, it brings to their memory the sum and substance of your argumentations so far.
Second, since this is a law trial, you will need to summarize also the law and how your case aligns with the law. Keep in mind that the average citizen does not know the law. Moreover, do not get bogged down with technicalities; you will lose people. In a plain way, show how the law applies to the situation.
Finally, you want to show how the application of the law favors your presentation and case. This is the most important part. You need to persuade people that your case is fully based on the law and that to uphold the law is to uphold your argumentation and your case.