Most state lawbooks contain statutes of limitations, setting limits on how much time can pass before states can no longer charge a person with a crime, or a person can no longer file a civil suit. After three years, or seven years, or whatever, form some offenses it's time to move on. There are exemptions, of course. There is no statute of limitations for murder, for example. It is too heinous a crime to simply allow someone to go unpunished if a case can be made even decades later.