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Omair Ahmad is a Delhi-based writer. His last book was Kingdom at the Centre of the World: Journeys into Bhutan (Aleph, 2013).

The limits of proof

ne of the most popular genres of both fiction writing and TV serials is the detective series. A crime is committed and then the good guys — whether the police or an enterprising detective — chase down the villain that did the evil deed. Their ability to do so depends on solving the puzzle from the few clues that the villain has left behind. To get away with the crime, the criminal has to make sure he or she has left not one trace behind. To solve the crime, the good guys have to correctly interpret just one clue. Traditionally, this has been the testimony of an eyewitness — often the victim of the crime — or a fingerprint found somewhere on the crime scene. Unfortunately, science tells us that these two forms of evidence are not at all reliable.

Dr Elizabeth Loftus at the University of California, Irvine has been researching false memories for decades. In the 1990s her research at the University of Washington revealed how easy it was for people, given the right nudges, would falsely "remember" cases, including that of "repressed" memories of molestation and violence by their own family members that were later found to be false. In other cases where police have caught criminals that they want the victims to identify, the police often unknowingly compromise the cases. Having worked very hard to capture who they think is the culprit, they cannot help letting their unconscious reactions to the perceived "criminal" show, influencing the witness to identify the person they think did the crime. According to Loftus' research approximately three-quarters of U.S. convictions on charges of murder and rape that were later overturned are those based on eyewitness testimony. It seems that just because we think we saw it, does not make it true.

In 2013 the Laura and John Arnold Foundation provided a $3,33,000 grant so that a team of psychologists and criminologists put together by the U.S. National Research Council to analyse eyewitness testimony. Their report, "Identifying the Culprit: Assessing Eyewitness Identification" was released in October 2014, and although cautiously worded, it states, "the fidelity of our memories to actual events may be compromised by many factors at all stages of processing, from encoding to storage and retrieval. Unknown to the individual, memories are forgotten, reconstructed, updated, and distorted... These limitations can produce mistaken identifications with significant consequences."

t seems that even if our eyes do not lie to us, our memory of what our eyes have seen is not something that we can rely on, certainly not in cases where we are sentencing people for crimes like murder. On the other hand, fingerprints, something that has been in use as a tool of forensic science for a century now, should be more reliable. Every person has a specific pattern of ridges and glands on their fingers. These are formed while the baby is still in the uterus, and they do not change throughout the life of a person. When fingerprint patterns are compared, the specific pattern of whorls and ridges are matched. Unfortunately, although the use of fingerprints has been admissible as evidence since as early as 1911, there is no set way that various agencies compare fingerprints. Furthermore, most times that fingerprints are recovered they are partial fingerprints, and smudged. Investigators therefore have a fragment of a clue, often a blurred fragment, and no set way of examining these fragments. This does not stop police claims of infallibility. In one case three highly trained FBI agents called the match from a partial print found on a plastic bag "absolutely incontrovertible" proof of the involvement of a lawyer from the state of Oregon in U.S. in the Madrid bombings. Except, of course, such a match was controvertible, and the print turned out to be that of an Algerian instead.

The difference between this and DNA evidence, which began to be used in courts in the late 1980s is striking. In the case of DNA evidence analysts take a set of short samples of DNA, usually 13 parts, and compare them. The chances of a random match would be approximately 10 million in one. The difference between a scientifically robust way of examining evidence and a scientifically weak one has been exposed by the Innocence Project, a non-profit NGO that was first set up in 1992 at the Benjamin N. Cardozo School of Law at the Yeshiva University in New York after it became clear how unreliable eyewitness testimony could be. Using the scientific rigour of DNA testing, the Innocence Project has helped overturn the convictions in more than three hundred cases, including those who had been sentenced to death for crimes they had not committed. In more than a hundred of these cases, the DNA evidence also led to the conviction of the person who had actually done the crime, demonstrating that good science can not just free the innocent but also catch the guilty.

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