Abstract: According to some commentators, an obscure genetic condition known as chimerism “could undermine the very basis of the forensic DNA system” and force a reconsideration of “the entire project of forensic DNA.” This conclusion is as unfounded as it is unnerving. Chimerism is a consideration in, but not a real obstacle to DNA identification. This essay explains why.
Saturday, March 23, 2013
Hot Off the Presses: Chimeric Criminals
Nearly two years ago, I raised a question about the depth of the documentation and analysis in the book Genetic Justice by Sheldon Krimsky and Tania Simoncelli. A discussion of chimerism and the threat it supposedly poses to DNA exonerations prompted the following debunking essay: Chimeric Criminals, Minnesota Journal of Law, Science, and Technology, Vol. 14, No. 1, Winter 2013, pp. 1-9. It is available from SSRN or on the review's website.
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I agree that chimeras due to natural or routine medical causes pose no significant threat to the utility of DNA identification, for the reasons you give: these mechanisms will not typically frustrate standard DNA sampling and will not fully mask one DNA profile with another's except in cases that are too rare to pose a remotely significant risk of error. However, there is one chimera-type scenario where the risk assessment is less straightforward: deliberate transplants of another's tissue into a suspect's body aimed at confounding DNA identification. (I realise this is very different to the scenarios you describe and stretches the meaning of a 'chimera', but it is somewhat similar to the 'temporary chimera' by blood transplantation that you mention in your article.)
ReplyDeleteOne such transplantation occurred in 1992, when a Saskatchewan doctor, Stephen John Schneeberger, inserted a plastic tube containing someone else's blood inside his arm prior to having his blood sampled in order to produce a false negative in a DNA identification exercise aimed at testing a rape allegation against him. His ruse deflected official scrutiny for years and was only exposed when his victim hired a private investigator to obtain his DNA covertly (in saliva and hair samples.) In the end, he was convicted not only of rape but also perverting justice and eventually lost his newly acquired Canadian citizenship.
This case shows how deliberate chimerism can indeed subvert the main DNA sampling process of the day, including fully masking the criminal's true profile. Schneeberger's ruse would have fully succeeded if it wasn't for the tenaciousness of his victim and his own further crimes (as Canadian courts initially refused to order further DNA sampling until he was accused of rape by his step-daughter.) On the other hand, this was a bizarre case from the early days of DNA identification and involved a criminal who was especially bold and resourceful (including having access to another's blood), a sampling process (blood sampling) that was especially open to manipulation (Schneeberger, claiming a rare illness, insisted on sampling himself) and a justice system perhaps too prone to dismiss rape allegations. The case also shows the difficulty of maintaining such a ruse in the face of scrutiny. The ruse itself required Schneeberger to engage in some (hindsight) suspicious behaviour at the time of sampling and was difficult to repeat. (He reinserted the tube with stored blood from the same source five years later when asked to provide a further sample, but the blood looked funny and didn't yield a profile. The ruse collapsed when a court ordered Schneeberger to submit to hair sampling.)
A repeat of this ruse today would have to target buccal swabbing. Although I've heard of some people putting some substances in their mouth to frustrate buccal swabbing, I'm not able to think of a technique that would plausibly yield a profile that would mask the true one. (But, then again, I would never have thought of the plastic tube trick either!) And the ruse would seem especially difficult for anyone other than a passing suspect to use. (For example, a long-convicted person seeking false exoneration by DNA would have been routinely sampled long ago.) There is surely a greater risk from non-chimeric ruses, such as planting someone else's tissue at a crime scene. (Indeed, such an allegation against the rape victim was Schneeerger's unsuccessful defence at his rape trial.)
Pertinently, unlike natural (or incidental medical) chimerism, the level of threat to the integrity of DNA identification is dependent on technological developments in subverting DNA sampling procedures (and the ability of investigators to counter those) as well as the resources and tenacity or criminals, matters that may change over time. So, this chimeric risk is one that, although slight at present and perhaps always, nevertheless needs to be constantly guarded against.
Thanks, Jeremy. Another variation might be called "romantic chimerism" resulting from passionate osculation. See Lingering Kiss: DNA Persists in the Mouth After Smooch, New Scientist, Jan. 26, 2013. Actually, I remember reading of a case in Europe, I think, in which a man tried to fool the police with his girlfriend's saliva in his mouth. However, I do not have a reference to the case handy. There was another attempt in the U.S. in which a man asked two friends for their saliva in the hope of tricking the police into thinking it was his. See Tony Reaves, Paris Arson Trial: Ex-girlfriend Says Breakup Behind Crime, Oxford Hills Sun J., Sept. 24, 2012.
DeleteAnother high profile case in this vein (although it doesn't sound quite so romantic!) is a by drink-driving / murder case from Long Island, where the accused was convicted of evidence tampering in relation to a buccal swab (in turn taken to test his claim of police tampering with a blood sample): http://www.nydailynews.com/new-york/dna-tamper-adds-time-dwi-murder-article-1.289012.
DeleteP.S. Some links on the Schneeberger case:
ReplyDeleteDNA warrant application (with a useful affidavit of known events preceding the big reveal): http://www.canlii.org/en/sk/skqb/doc/1999/1999canlii12790/1999canlii12790.html
Conviction: http://canlii.ca/en/sk/skqb/doc/1999/1999skqb208/1999skqb208.html
Appeal against conviction: http://canlii.ca/en/sk/skca/doc/2000/2000skca118/2000skca118.html
Appeal against revocation of citizenship: http://www.canlii.org/en/ca/fct/doc/2003/2003fc970/2003fc970.html