Statute of Limitations laws limit the time for prosecution of criminal charges and civil complaints.
I am not a lawyer, but from my reading and common sense, statutes of limitations were set up to prevent harassing/wasteful prosecution and to ensure that those accused of crimes can properly defend themselves by calling on witnesses and bringing forth other evidence in their defense. Imagine prosecution commencing on, let’s say, an 8 1/2 year old case. Since all criminal charges must be proved beyond a reasonable doubt, it is unreasonable to believe that any witness can accurately describe events, feelings or other personal accounts for long periods of time, no matter how traumatizing. People forget, learn, and change their opinion. Cases of great age must therefore be supported with much more physical evidence . Written statements can be used, however, can be influenced by surrounding circumstances such as shock or fear of punishment.
Statute of limitations are usually set by severity of crime and differ by state. Less serious offenses such as infractions and misdemeanors have shorter time frames in which charges must be filed. Some states require that prosecution must only commence (by filing a warrant for arrest), while others may require that formal charges be brought against the defendant at arraignment before requirements are met.
Tolling, or a pause in the Statute of Limitations, occurs in most cases when a defendant is engaged in similar illegal activity or when they have left the state in which the crime has been allegedly committed. Time begins to resume when the defendant resumes conducting business in state.
This is not absolute, however, and has been found that “If the authorities fail to discover a criminal living in the open within a specified amount of time, society has determined that at that point the criminal should be able to live free from the possibility of prosecution. It appears that this notion is born out of a sense of mercy more than pragmatics: if the criminal is a fugitive, out of the state in which the crime was committed or otherwise living in hiding, this tolls, or suspends, the statute. (Once the criminal reenters the state the statute resumes running.) However, if the criminal were living an open, public, so-called “reformed” life, after a reasonable period of time he is allowed to be free from capture.” – USLegal.com
It is logical, seeing that Statutes of Limitations were created to both protect those accused of crimes and the public financial resources, that as long as a defendant remains diligent in maintaining their defense, that the State or plaintiff must also maintain prosecution. This means that they must respond to the defendant’s claims, inquiries and such, made in good faith, to ensure that evidence remains fresh or otherwise relevant to the case. More serious crimes require greater burden of proof, usually evidence less prone to decay (i.e. physical evidence as opposed to statements), hence the longer Statutes of Limitation for Felonies, and indefinite time for murder.
If the plaintiff fails to maintain prosecution, they give up their right to continue charging the defendant and society deems that person to be free of further negative action. This prevents a defendant from ever being tried without the constitutional right to a fair and speedy trial. The burden of proof remains on the prosecution, and the have given up by abandoning the charges.