DNA as Identity


This KSL TV news report is about Clearfield police filing charges against an alleged rapist based on his DNA. The catch is that they have no suspect; no person who the DNA belongs to. Just the same DNA in two rapes. The name on the charges will be "John Doe." This is an excellent case study in identity.

Identity is a set of properties. Collect enough properties and only one individual has them all. For example, if the only property I have is that the first name is "john" or eye color is "blue" then there are lots of people who might fit that bill. If the first name is "john" and the eye color is "blue," I've narrowed it down some. Add more properties and eventually I get a set small enough that they apply to only one person. DNA is just a compact representation millions of properties. Identity theft is acquiring enough of someone else's properties (and lying about the rest) that you can substitute for them in certain transactions.

As I've said before, courts are in the identity business. A court of law is largely an exercise in convincing a group of people that some person has a set of identifying properties (those associated with the evidence of the crime). In the case reported by KSL, the charges are being filed based on a set of properties that doesn't happen to include a name--just the DNA. Unusual? Yes. But not necessarily wrong.