Not Quite Sherlock Holmes: Why Law Enforcement Resists Science

Per the Jurist article posted here by guest columnist David Harris, the assistant dean of research for University of Pittsburgh School of Law, there is a documented resistance by law enforcement to advances in scientific knowledge that undermine more “traditional” methods of police investigation.  Thus, despite the benefits of science to police work depicted to the public in numerous articles, movies, and tv shows, law enforcement generally does not embrace existing scientific work, with the exception of DNA and certain kinds of classic chemical analysis.  The article stresses the fact that police and prosecutors in the US resist science.

The scientific work referred to in the article includes testing of eyewitness identification and forensic methods such as fingerprint identification. According to the author, tests have proven these methods to be inaccurate and in need of verification for some time.  The author suggests that by implementing some established tests, the quality of the testimony and evidence provided would be greatly improved, but that American law enforcement continues to resist this science and refuses to change its basic tactics to reflect the best of what science has to offer.

The author cites his book as to an explanation of why this resistance takes place. The article then goes on to cite the history of modern science in law enforcement and the benefits of DNA evidence to the field. Specifically, it cites the 300 DNA-based post-conviction exonerations in the US to date, an indication of startling patterns hinting at much bigger problems. “Among the 300 cases, 72 percent contained an incorrect eyewitness identification. Half of the cases contained faulty (non-DNA) forensic work. And 27 percent feature a false confession or statement of guilt at some stage.”

The article also descries problems with eyewitness identification, false confession due to interrogation, and fingerprint/tool mark indentification. The author blames cognitive dissonance for this. However, this is where the author and I diverge.  Police work hard to nab the bad guy.  All of the science suggested by the author is designed to demonstrate error in that work.  Now certainly I am not trying to state that the members of law enforcement want to put the wrong person behind bars.  Rather, I am trying to point to a certain conflict between theory and practice that has existed for decades.  The same tension exists between practitioners and theorists in many fields (lawyers and law professors, perhaps?).  Police and prosecutors are practitioners.  They don’t want their work second-guessed by theorists.  Perhaps this is unwarranted, but there is another reason for this tension.

The other reason is that law enforcement is working against the system. The legal system starts with a presumption of innocence.  It further tilts the system against the prosecutor and the policeman by requiring proof of every element of actus rea and mens rea.  If a single element isn’t proven, no conviction.  Thus, if one were to commit a crime that the prosecution failed to secure an indictment for, the criminal would not be guilty.  Finally, the jury system is supposed to operate on a preponderance of the evidence, not the mere civil standard.  Enhancing this point is the fact that both federal law and half of the states require a unanimous jury verdict.

So, prosecutors and police work hard to put people behind bars, but the system is against them.  Why are we surprised that they don’t want people to contest the basic tools of their trade?  Why should this law professor wonder why law enforcement doesn’t want more tests to inspire doubt in the evidence, when it is likely that such evidence is not 100% conclusive itself?  Even the author admits that the tests aren’t 100% accurate (what in science is?)


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