DNA Expert Witness On Scientific Evidence

DNA expert witness Dan E. Krane of Forensic Bioinformatics, Inc. on scientific evidence:

What makes scientific evidence so powerful in court is very simple: it’s supposed to be scientific. That means that it is supposed to be objective and completely independent of the subject of an investigation (a suspect or a defendant). It is therefore absolutely shocking that DNA testing laboratories routinely put themselves in a situation where specific information about a subject’s DNA profile might influence their interpretation of an evidence sample.

Last December, eleven prominent experts from around the US and even Scotland met in Washington, DC to discuss the problem of examiner bias/context effect in DNA profiling. Given the breadth of expertise and roles of these experts it surprised many of us that we were able to not only agree about the magnitude and nature of the problem, but also to a solution. The result was the generation of a position paper that has been published in this month’s Journal of Forensic Sciences.

Our bold and surprisingly controversial recommendation is the essence of simplicity: analysts should interpret evidence samples, at least initially, without any knowledge of the DNA profile of any suspects being investigated. Arguments to the contrary are ludicrous and are generally equivalent to a student demanding to see an answer key prior to taking an exam because that makes it so much easier for them to come up with the right solutions. Information about a suspect’s DNA profile does help with the interpretation of evidence samples in the resolution of surprisingly common ambiguities that lend themselves to a variety of alternative interpretations. But, using a defendant’s profile in that way is unequivocally wrong and invariably works to their disadvantage at the same time that it seriously undermines the scientific nature of the test.

Please help us spread the word that DNA profiles should always be interpreted objectively. More information about the authors of this position paper and the opportunities for subjective interpretation of DNA evidence is available at the Forensic Bioinformatics web site (www.bioforensics.com). It will also be a topic for discussion during our annual meeting coming up in just a few more weeks.