Each individual has a unique DNA "fingerprint" based on the sequence of the A, T, G and C nucleotides in their genome. These differences allow scientists and criminologists to compare samples containing DNA (hair, blood, semen, stone age skeletons) with DNA from specific individuals. Beyond the obvious uses in criminology and paternity testing, this also is useful in reconstructing molecular genealogies and tracing the dispersion of specific Y-chromosome markers. For example, the Lemba tribe in southern Africa which had an oral history of Judaic descent was confirmed to have a much higher incidence of a Y-chromosome sequence that is found in the priestly lineage of Aaron than surrounding populations. Even though the Lemba tribe appears completely African, because of the father-son pattern of inheritance of the Y-chromosome it has remained present in their population unaltered for centuries. Other studies have suggested that Genghis Khan and his sons have ~16 million male descendants on the earth today and that ~8% of Irish men share the Ui Neill clan marker.
For me, the most striking contribution of DNA fingerprinting is its use in overturning wrongful convictions. For a real eye opener go visit the Innocence Project website. You can click on your state and read about every case of wrongful conviction overturned by DNA evidence (251 post-conviction exonerations to date nationwide). You can also see if your state offers any compensation for wrongful conviction (mine doesn't) or even requires samples that contain DNA evidence to be saved for future reference (mine doesn't). The unavoidable conclusion of all this is that the death penalty has will probably continue to result in the execution of innocent individuals.