Being a prosecutor is about making decisions--life changing decisions. That young man who got arrested last night has his fate in your hands. Will he be able to enlist in the military? Can he go to college and pursue a profession? Or is he going to spend the next few years as a guest of the state? You will have a huge say in how he spends the rest of his life. It's not within us to make perfect decisions every time, but we can always strive to make the best possible decisions under the circumstances.
When you look at that file, ask yourself four questions:
1. Has a crime been committed? Not every wrong is a crime.
2. Did the defendant commit it? Never, ever rubberstamp the decisions of others. Perform your own evaluation of the available evidence.
3. Can you prove it? There is a wide gap between knowing someone committed a crime and being able to prove it beyond a reasonable doubt. You should never file a case unless you have a reasonable prospect of conviction.
4. Is the case worthy of prosecution? Although a defendant may be guilty of a breach of the law, and although you have a reasonable prospect of convicting him, sometimes justice is better served if you decline to prosecute. Every unconsented touching is a battery, but it would be silly to prosecute every person who ever laid his hands on another without first getting a written consent form.
There are other questions you should ask before filing charges, but these four are foundational.