There is an aspect of American law which is not often covered in Law-and-Order type shows - the statute of limitations. Most crimes have a length of time in which they must be prosecuted. If the State is unable to try a suspect by that time limit, it is out of luck.
Defense attorneys argue that statues of limitations exist for a reason -- if a person is charged with a crime after too long a period, it may be difficult to defend against the charges. "People’s memories fade" and "witnesses move and can’t be found," Bauer reports at the KC Star.This is an important protection in our system where any suspect is "presumed innocent until proven guilty". (Please note, capital crimes like murder have no statute of limitations.) But a new disturbing trend is beginning to emerge. Prosecutors looking to get around the law by charging the DNA found in crimes in absence of an actual person. This allows the search for an actual person to go on indefinitely, and effectively removes a critical protection in our legal system.