Writing a mitigation letter means you're asking the court for leniency in sentencing. Judges are free to consider almost any circumstance that justifies a lesser punishment, from lack of a prior criminal record to a recent bereavement that put you under emotional stress. Mitigating circumstances typically fall into two categories: facts about the crime and facts about the offender.
TL;DR (Too Long; Didn't Read)
Focus on explaining who you are and why you acted out of character, or if there were very unusual circumstances when committing the offense. Show the judge that you're worth a second chance.
Start With the Basics
Begin by writing the name of the presiding judge and the court in the address block, followed by the case name and number. Include the date. Open your letter with the salutation "Your Honor" or "Dear Honorable Judge Jones." In the opening paragraph, briefly describe why you're writing and the circumstances behind the incident.
Explain the Mitigating Circumstances
In the body of the letter, explain the mitigating circumstances. For example, you might tell the judge that you only played a minor role in the crime or that you acted out of necessity when stealing food for your starving family. Or you might explain that the victim was also culpable by starting the fight in which you were involved. If you acted out of character, explain why. Were you having problems in your personal life that affected your behavior or were you suffering unusual stress at the time of the offense? If this is your first offense, be sure to mention your lack of a prior criminal record.
Don't Throw the Kitchen Sink At It
Not everything is a mitigating circumstance, and what you're not doing is making excuses for the crime. The last thing a court wants to read are reasons why you think your behavior was justified. Judges don't want you to recommend your own punishment, either – a judge is unlikely to grant leniency if you are only writing because you're scared of doing time. Stick to the situations that influenced your behavior in some way so the judge gets a better understanding of why you acted the way you did.
Show Genuine Remorse
Genuine remorse is a mitigating factor in its own right, so be clear that you've accepted responsibility and showed remorse. If you confessed upon arrest and have been helpful throughout the proceedings, you likely have this factor in your favor. Be honest, sincere and contrite. Where possible, explain some of your positive attributes, such as your goals and achievements in life that show that ordinarily, you're a model citizen. Do so with prudence, however. You want to give the judge the facts, not your whole life story.
Focus on the Future
Finish the letter by explaining how the penalty will affect your life. For example, if you're a poor student struggling to pay tuition, a heavy fine could be detrimental to your career prospects in the long run. If drug or alcohol addiction contributed to the incident, explain how you're making an effort at rehabilitation. Judges are human, and it's perfectly possible they will grant leniency if the maximum sentence could harm your future life chances.