Which Twin Did It? New DNA Test May Have the Answer

By Christopher Coble, Esq. on March 05, 2019 | Last updated on March 21, 2019

It's a classic legal defense, at least for soap operas: "My evil twin did it." And, until recently, it was pretty effective. Standard DNA tests couldn't distinguish the good twin from the bad one. But that might be changing soon. Researchers at a Brussels laboratory testing company headquartered in Brussels claim they were able to distinguish enough mutations in the genomes of two twin brothers to tell them apart.

And that test may soon be coming to American criminal courts.

Fraternal DNA

As The New York Times' Carl Zimmer describes: "In recent years, scientists have gained a clearer picture of the early development of the embryos of identical twins. Originating from a single fertilized egg, they later acquire unique genetic mutations. New advances in DNA sequencing are making it possible to pinpoint those mutations -- and to tell identical twins apart." While the need for these tests are rare, when they are required it's usually in serious cases of paternity and rape investigations.

Zimmer notes rape cases in Boston, Massachusetts and Grand Rapids, Michigan that stalled because existing DNA tests couldn't distinguish between twins. When prosecutors in Boston tried to admit evidence from the new DNA test in court, the judge ruled that it was too new -- it had yet to be replicated by any other researchers or subjected to peer-review. (In order to be admissible in court, scientific evidence must meet several factors, including whether the technique can be or has been tested, whether it has been subjected to peer review, whether the test procedures have been published, whether the test has a margin of error and, if so, at what rate, and whether the technique, as applied, conformed to existing standards for the test.)


Thus far, the twin DNA test has not been used in a U.S. criminal court. Researchers and prosecutors agree the test will need to be replicated in several other labs and across many other sets of twins before judges will find it reliable. The good news, however, is that DNA testing hasn't suffered the same scientific scrutiny as some other CSI-style forensic evidence.

So, the day may be coming when your evil twin defense doesn't hold up. So you'll probably need a better one from an experience criminal defense attorney.

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