From "Law and Order" to "CSI," not to mention real life, investigators have used fingerprints as the gold standard for linking criminals to a crime. But if a perpetrator leaves prints from different fingers in two different crime scenes, these scenes are very difficult to link, and the trace can go cold.
Excepting of course identical twinsEdit: apparently I was wrong
They tend to have different fingerprints for the same reasons they will have differing birthmarks.
Identical twins do not have identical fingerprints, because fingerprints are not only genetic. They might be close or somewhat similar, but rarely identical. They can be distinguished as different individuals by regular pedestrian forensic techniques.