25 October 2011

How DNA convicted and ultimately freed Amanda Knox

By Gabrielle Carbonara, Juris Blogger
Four years ago, when Amanda Knox, Raffaele Sollecito, and Rudy Guede were convicted of the murder and sexual assault of British exchange student, Meredith Kercher, the Italian Government’s case relied largely upon DNA evidence.  While appealing their arrest and conviction, it is this evidence that was the primary issue.

According to the Italian government, DNA belonging to both Knox and Sollecito, an Italian graduate student, was found on a a bra hook belonging to Kercher and on the handle of a knife that was allegedly used in the murder.  On its face, this seemed like an open and close case; the police found the couple’s DNA meaning there was less than a one in a million chance that anyone could have committed the murder. This case, however, was not as simple as it seems.

The case rested on poorly collected and contaminated DNA evidence which was analyzed using a process called Low Copy Number (LCN).  This process is completed by using a very small sample and then copying each component found and assigning that component a number.  An article on Legalweek.com described the process as a fishing expedition, where “a small drop is turned into pond and the experts go fishing for components and try to agree which components are present.”  This process can be unreliable because each dip into the sample could have a different component and the components that appear most frequently are the ones that are included in the sample.  Sometimes a statistic is given to show how many other people could likely have the same DNA.  If such a statistic is unavailable, though, these samples could still be used to show that the accused person was not excluded as a suspect even though it could not be ascertained how many other people could also be included as a suspect.

Here, both defendants’ DNA was found on the bra clasp and on the handle of a typical kitchen knife, which, incidentally, was found in a kitchen drawer and said to not have been the actual murder weapon.  These DNA samples were microscopic.  Independent experts said that the Italian Police had poorly handled, collected and analyzed the evidence which put Knox and Sollecito behind bars, for 26 and 25 years, respectively.  Experts from the United States also reviewed this DNA evidence and expressed their concerns that the Perugia police mishandled the samples.  In addition to the suspicions that the evidence was poorly obtained, Discovery News reported that the Italian prosecutors “used a DNA detection limit far below that of the independent U.S. experts or the FBI in determining the presence of blood DNA on the blade, which made contamination a much more likely source of the genetic material.”

It seems that the Italian police and prosecutors were anxious to find Kercher’s murderers and forced the evidence to quickly fit their theory, that Knox and Sollecito were a young, sinister couple who viciously assaulted and murdered Knox’s roommate, rather than carefully and correctly collecting the evidence and allowing it to lead them to the true murderers.  Although what actually happened the night of Kercher’s murder has still not been determined, earlier this month an Italian appellate court acquitted Knox and Sollecito and the two were released after spending four years in an Italian prison.  The third defendant, Rudy Guede, is still serving a 16 year sentence but maintains he is not responsible for Kercher’s death.

Gabrielle Carbonara is currently a 2L at Duquense University. She is a student administrative assistant at the Duquesne University School of Law Career Services Office, the Treasure of the Italian-American Society and the Academic Chair of Phi Alpha Delta. Gabrielle earned her undergraduate degree at Duquesne University in Sociology with a concentration in Criminal Justice and a minor in History. She will graduate from Duquesne Law School in 2013 and can be reached at carbona1@duq.edu.