Criminal DNA “testing” is not a matching of the entire genetic makeup of an individual (which is unique), but is a matching of a “genetic profile”, a small (13 loci) piece of the full genome of the individual. Over the last couple of years questions have been raised about whether the FBI estimated odds of unrelated people sharing profiles is 1 in 113 billion or if it is in fact a much more likely event.
A recent article in the LA Times lays out the case for lower odds. It relates that a 9 of 13 loci match is really not all that rare of an event even between two folks that appear quite different and have no demonstrable relationship. The article also points out that a 13 out of 13 loci match in a pair of unrelated folks may be a possibility as well.
It should be noted (as in the article) that officials do try to match all 13 out of 13, but at times fewer loci are available for comparison depending on the specimen or sample.
Our justice system relies heavily on the FBI odds estimate. We owe it to our citizenry to be more certain that it is based on “good” science. We need to prove that we can be confident in that odds estimate. We need to seek the evidence, the proof, just as the article calls for further study, a study that really should not be all that difficult to do.