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Friday, May 14, 2004

A Forensic Conundrum 

As a would-be forensic biologist, one subject that interests me, and occasionally galls me, is the assumption that DNA is the "magic bullet" of forensic science, that it will solve all and quickly at that. Then there are cases like this:
GRAND RAPIDS, Mich. (AP) - Police thought they had solved a 4 1/2-year-old rape case when DNA evidence from the assailant matched that of a prison inmate.

Then they realized the inmate, Jerome Cooper, had a twin brother who could have the same DNA.

Both Jerome and Tyrone Cooper, 36, were in the Grand Rapids area at the time of the 1999 rape of a college student, and both are convicted sex offenders.
Since matching Jerome Cooper's DNA, police have been searching for Tyrone Cooper to determine whether the twins are fraternal or identical, and if they have the same DNA. A warrant has been issued for Tyrone Cooper's arrest, charging him with failing to update his address on the state's sex offender registry.

"Our big hope in this case is they are fraternal," police Sgt. Timothy Williams told The Grand Rapids Press.

As the article indicates, identical twins have 100% concordance in their DNA sequence, and so if it turns out the Cooper brothers are identical, the cops are stuck. Same DNA--two different people. How do they get around this?

That the answer might prove to be a difficult find shows that there are severe disadvantages to making forensic science a technology-based, or database-intensive, discipline. My former professor, Peter De Forest, always waxed eloquent, both in class and outside, about how criminalistics--the field of gathering physical evidence and the fundamental science that every other forensic discipline is based on--is in decline, its techniques losing its impact in the wake of new technologies, new toys, and databases. The first time I heard his line of thinking, I blanched, because hey, I loved DNA and thought it to be practically god-like. Thankfully, I came around to De Forest's way of thinking as time went on, and came to the realization that a case cannot be solved by tools alone; there must be an overall framework and context, something that is dynamic and subject to constant change.

So what of the identical twins and how to distinguish between them? The answer, perhaps, lies in a powerful field, but one that has taken a severe beating in the courts in the last little while: fingerprints. Until otherwise proven, each individual has his or her own unique set of prints--even identical twins. So if the original crime scene techs were smart, and the evidence had been kept in storage all this time, perhaps some useful prints were obtained back in 1999. There's also the old-fashioned gumshoe approach, interviewing people, accounting for each of the twins' whereabouts before, during, and after the crime took place.

But chances are, alas, the resolution of this case will hinge on finding that other twin and waiting for the DNA test to show--one way or another--if they are fraternal or identical.

And if it turns out to be the latter situation--well then, things might just get a little more difficult.

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