Sunday, February 08, 2009

DNA Has No Voice: DNA Does Not Cry Out "Innocence" (or "Guilt")

An article in today's NYTimes states:
Cases that lack what many call the “magic bullet” of DNA often require cumbersome investigations, including finding and re-interviewing witnesses or poring over thick files to find anything vital that a trial lawyer might have missed. Even when crucial evidence is uncovered — witness recantations or exculpatory statements that were ignored by prosecutors — judges, juries and prosecutors often treat it with skepticism.
The above statement reflects a fundamental misunderstanding of the logic of DNA evidence. Like fingerprint evidence, footprint evidence, or any other such evidence, DNA evidence does not speak on its own: it does not, by itself, proclaim "innocent" (or "guilty"). Like fingerprint evidence etc., DNA evidence speaks to innocence or guilt only within a factual context. And that context is sometimes or often contested. For example, a fingerprint or a residue with DNA may have been deposited at the scene of the crime at the time of the crime or the fingerprint or the DNA may have been deposited there at some other time. Alternatively, the person who deposited a fingerprint or DNA at the scene of the crime at the time of the crime may or may not have intended to kill, for example. Alternatively, investigators may have found a fingerprint or DNA of one culprit but not another. Alternatively, one culprit may have stood by while a co-culprit engaged in sexual intercourse with the rape victim. And so on ad infinitum. DNA is not a "magic bullet" that groks guilt or innocence. Only Star Trek machines do that.


the dynamic evidence page


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