DNA is sensitive and a great forensic tool, since every one of us is unique. But most DNA comes from someone who actually exists. Phantom DNA is only in one's imagination....or is it?
Today there's a story about Germany's most wanted woman, a serial killer for whom the German police have been searching for 15 years. The same DNA was found at many of this woman's vicious crime scenes, something like 40 in all.
Unfortunately, it now appears that there is no such person! Or at least that this person isn't the serial killer the police have been looking for for so long. It seems that the cotton swabs used to collect the DNA may have been contaminated by DNA from a worker at the swab factory.
This points out one of the problems with amplifying minute amounts of DNA: contamination. Contamination plagued studies of ancient DNA for quite some time, and still makes aDNA work a game for experts rather than amateurs. People concerned about bioethical and societal issues involved in forensic DNA (and millions of CSI fans, presumably), raise the issue of contamination, and the German experience shows that the problem can be an insidious one.