Lt. Mark Spaetzel, the lead investigator of Amy's case, has always said that one day new technology might solve her murder. Maybe this is what he was talking about.
Seems scientists are getting close to using DNA to re-create the face of the person who left it behind. Meaning, if they, in fact, have DNA taken from the crime scene, or under Amy's fingernails, one day soon (5 years, 10 years?) we'll be able to see that person's face.
A heads up to the killer: if you don't confess before they have you cold, you're gonna get the death penalty.