STL defense claims confirmation bias in cell analysis
The Daily Star
03
May
2017
During expert witness John Edward Philips’ testimony at the Special Tribunal for Lebanon Tuesday, defense counselors for Hassan Merhi questioned the methods Philips used to determine the locations from which various cellphone calls were made. Cellular data, such as the information Philips analyzed over the course of his testimony, has been crucial to the prosecution’s case against the five defendants accused of planning and executing the 2005 bombing that killed former Prime Minister Rafik Hariri and 21 others. Investigators and prosecutors have used the movement and coordination between various cellphones to track the alleged plot in the lead-up to the attack, and identify the defendants. Much of Philips’ previous testimony detailed his methods to demonstrate that, in several cases, multiple, seemingly unconnected, phones were in fact used by the same individual. But defense counselor Jad Khalil attempted to poke holes in Philips’ testimony by asserting that the prosecution didn’t account for the fact that many different cell sites could serve a particular geographic location – making it difficult to claim one phone was in any particular location at one time. “Isn’t it true to say that your maps do not indicate the possibility that many different cell [sites] could also serve and cover a particular location?” Khalil asked. Philips agreed that this could be true and that a number of factors played into the range of a site’s cellular coverage – including cellular antenna power, the height and orientation of nearby buildings and the surrounding terrain. Later in the session, Dorothee Le Fraper du Hellen, the second counsel for Merhi, also attempted to cast doubt on Philips’ testimony. When conducting analysis on a series of phones allegedly connected to a single unidentified subject in the case, Philips only received call logs for a distinct period of time: between Sept. 24, 2004, and Feb. 27, 2005. By his own account, Philips was only tasked with either confirming or disproving the fact that these phones were attributed to the individual – not with conducting a bottom-up investigation of the call logs. Because of this, Le Fraper du Hellen accused Philips – and the prosecution broadly – of confirmation bias. “You will agree with me that what you were commissioned to do at the time was more a confirmation analysis than an investigative analysis,” she said. “In order to complete your analysis, why did you not ask the prosecutor to provide you with the whole table of calls?” she asked. In response, Philips noted his role in the investigation was narrowly circumscribed, and that the job of identifying the numbers and phones was carried out by others on the prosecution team.
