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Let the DNA Fit the Crime


Yet another important issue raised by Krimsky and Simoncelli is the problem of technical care and competence, both in collecting samples at crime scenes and in their analysis in police laboratories. There is a great variation in the technical care and competence among various local laboratories. In New York City there is relatively careful quality control. For example, for every DNA crime sample that is analyzed there must be a control run involving a known DNA sequence; and the FBI will not report an analysis based on fewer than ten STR sites. But such ample resources and the scrupulousness of laboratory technicians are not uniform throughout the country. An independent quality control report on the Houston Police Department’s crime laboratory found that among 135 DNA cases reviewed, 43 involved serious analytic errors.

The widespread use of DNA profiles by the police has led, in a number of countries, to the establishment of national computerized data banks to which local departments can contribute and refer. These record the DNA profiles of people arrested, whether or not they have been convicted of a crime, and of DNA collected at crime scenes. In the United States the FBI manages such a database, the Combined DNA Index System (CODIS), which currently contains over eight million records. CODIS, or a similar database in other countries, is used in “dragnets.” If DNA is recovered from a crime scene or taken from anyone remotely connected to a crime, it can be used to search CODIS. If there is a perfect match, a prime suspect has been identified from what is known as a “cold hit.” In case this suspect had already been imprisoned or is dead or otherwise physically removed from any possibility of having committed the crime, one must assume that a laboratory error or a contaminant during the investigation is the source. Putting aside such annoying situations, all other evidence exculpating the suspect is explained away or ignored.

A second form of dragnet does not require perfect matches in CODIS but is based on social presuppositions including racial profiling or on geographic proximity. For example, in a serial rape investigation in Miami, a dragnet by Florida officials asked more than 120 Hispanic males to provide DNA samples, and in Ann Arbor, Michigan, police asked more than 600 black men to submit to DNA testing in another serial rape case, of whom 160 agreed. The latter example exemplifies an important issue in civil liberties and the legality of searches and seizures. The police chief in Ann Arbor threatened that anyone who refused to submit a sample would become an active suspect in the case.

While the probability of finding two unrelated people with the same complete thirteen-site DNA profile is essentially zero, close relatives may have the same profile for part of the thirteen sites. This creates the possibility of “familial searches” for relatives of the actual criminal who might then lead to a final resolution of the case. While only identical twins have identical profiles, full siblings will share, on the average, half of their alleles, as will a parent and offspring, while cousins will share a quarter. Once a group of likely relatives of the guilty person has been identified, the police may then narrow down their search sufficiently to use other information in their search.

Partial-match dragnets and familial searches raise serious issues of civil rights. Both involve taking DNA from the bodies or secretions of persons who have not voluntarily come forward with an offer of their saliva or blood. In many cases a great deal of pressure must be applied in the form of threats against people who have not themselves been charged with any crime, as in the Ann Arbor case, or else there may be surreptitious sampling of objects in their possession. For Krimsky and Simoncelli these are all forms of searches and seizures without legal warrant that are forbidden by the Fourth Amendment. If the police cannot enter my house and search through or seize the physical objects contained in it without a legally obtained warrant, surely my body must be so protected. There is even the question of whether the cells and hair that I shed, the saliva that I deposit on the flap of an envelope, and the feces that I eject are “abandoned” materials and therefore are freely available to investigative authorities (or anyone else who cares to have them). Thus far, the courts have held them to be so, although it is unclear how the judges would proceed against persons who wished to maintain their proprietary rights.

While DNA analysis has become a major tool for the apprehension and conviction of people who have committed acts of violence, it has also led to the exoneration of those who were falsely accused. Krimsky and Simoncelli have both been deeply involved in the struggle to exonerate the innocent. Their book, as might be expected of them, contains chapters on such topics as “Privacy and Genetic Surveillance,” “Racial Disparities in DNA Data Banking,” and “Toward a Vision of Justice: Principles for the Responsible Uses of DNA in Law Enforcement.”

Having read the last chapters of Genetic Justice, one should then turn to Convicting the Innocent by Brandon Garrett, a book devoted to the deliberate use of DNA primarily as a tool for exonerating and freeing those who, for whatever reason, have been falsely convicted and punished. Garrett’s book arises from his longtime association with Barry Scheck and Peter Neufeld, founders and directors of the Innocence Project, whose purpose is to overturn false convictions through the use of DNA evidence. As of this year more than 250 people, convicted of a variety of serious crimes, have been exonerated by the use of DNA, many of them after years in prison and even the threat of execution.

One of the ironies of that history is that Scheck and Neufeld, together with the author of this review, originally opposed the use of DNA evidence. That is because, in its early stages, DNA identification used DNA variants that differed very much among ethnic and racial groups in their relative proportions. An example was the murder, in a trailer park in northern Vermont, of an Abenaki Indian woman. About a third of the residents of the trailer park were Abenaki in a region with many Abenaki. They have proportions of the various DNA variants that are quite different from Caucasians. An accused Abenaki had DNA that matched blood from the crime scene, but the trailer park is on a main north–south tourist route. So whose population frequencies should have been used in making a case?

All that has changed now. The differences in proportions of the DNA variations currently used in forensic analysis make only a trivial difference in conclusions about incrimination. The Innocence Project can exculpate people beyond any reasonable doubt without having to make arguments about ethnic group differences.

Garrett has chosen to illustrate the various sources of injustice in prosecuting and convicting innocent people. These include false confessions extorted by extreme psychological pressure on vulnerable people who are promised relief (as with the Central Park Five, among many others); misidentification by eyewitnesses who are themselves under police pressure; eyewitness identification from carefully stacked lineups and subject to police management; flawed forensic tests that include hair matching, shoeprints, fingerprints, and voice matching; and out-and-out lying by witnesses or jail informants who have something to gain by making things up.

A uniquely valuable part of Garrett’s book is a statistical appendix that provides a quantitative overview of the false convictions, their consequences, and the factors that contributed to them. For example, 47 percent of exonerations occurred between sixteen and thirty-five years after the original convictions. Of those exonerated, 62 percent were black, and 89 percent were accused of rape. In 74 percent of cases forensic evidence was presented against them and 76 percent of convictions were backed up by eyewitnesses. It is hard to imagine seven pages more damaging to the claims of our system of criminal justice, a system in which careerism is deeply embedded.

In a recent issue of The New York Times Magazine a leading state’s attorney for Lake County, near Chicago, when asked by a reporter for The Chicago Tribune about what seemed to be contradictions in a case, is quoted as replying: “The taxpayers don’t pay us for intellectual curiosity. They pay us to get convictions.”3 I was immediately reminded of Floria Tosca’s words as she contemplated the fallen police chief Scarpia: “Avanti a lui tremava tutta Roma.” Before such prosecutors all America must tremble.


Saved by DNA June 7, 2012

  1. 3

    Andrew Martin, “The Prosecution’s Case Against DNA,” The New York Times Magazine, November 25, 2011. 

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