Criminal cases, with the exception of murder or other crimes resulting in the death of the victim and a few other excepted situations, have a statute of limitations. After the limitations period expires, usually three to six years after the commission of the crime, the defendant has a nonexculpatory defense to criminal prosecution based upon the passage of time. That means they can be relieved of criminal liability even if they are guilty of committing the crime. As a result, sex crimes involving children often expire nine years after their commission in the absence of DNA evidence linking the victim and the defendant.
Limitations periods are usually established to force law enforcement to timely act on evidence and investigate and bring charges quickly so the best evidence is available. From a practical standpoint, evidence and witnesses tend to disappear over time, so this makes sense. Opponents of limitations periods frequently indicate that for some crimes, society’s interest in retribution and justice will exceed the time period provided in the statute of limitations. This is perhaps most acute in the case of sex crimes and crimes involving children. But even if damning evidence was found linking Heinrich to a sex crime with Wetterling 25+ years ago, but not also Wetterling's murder, the statute of limitations periods will have run. This would likely lead commentors to push for the legislature to extend the limitations period to allow the prosecution to move forward. However, it is not constitutionally permissible to extend a statute of limitations period after that period has run - the constitution prohibits ex post facto laws, i.e. laws which punish an act after the act has already been committed.
Many Minnesotans and others across the country will be closely monitoring this investigation as Wetterling's 1989 abduction, and the ensuing public reaction, reshaped how Americans raised their children including the concept of "stranger danger" and the creation of the AMBER alert system.