The Soham murders involving Jessica Chapman and Holly Wells was one of the most high profile cases to be reported and documented in the last ten years. Cell site analysis played a critical part in the investigation throughout and ultimately helped to convict Ian Huntley of murder.
Cell site analysis aims to determine the geographical location of a mobile phone through analysis of data records, transmit and receive beacons (cell sites) and signal strength of a specific area. Although not an exact science, it is a technique that can be applied by expert witnesses to help defend or prosecute a suspect during a case relying on mobile phone evidence.
Statistics show that in December 2008, over 75 million mobile phones were active in the United Kingdom alone. This figure confirms a larger portion of mobile phones today than there are people (estimated 62,041,708). It is therefore no wonder that Cell Site Analysis (CSA) is an increasingly important forensic and investigative technique used in the UK today.
During the investigation in Soham, Police questioned all males about their whereabouts at the time of Holly and Jessica’s disappearance and asked for a contact mobile number. Ian Huntley initially insisted that he had been out of Soham at the time that the alleged incident occurred. However, phone records and cell site analysis in the area suggested that Huntley’s phone had been used in the vicinity of his home and that one of the girls phones had been switched off in the same area around the time of disappearance. The combination of this evidence, general policing and the investigation eventually lead to the sentencing of Ian Huntley.
Cell sites, or ‘masts’, are often placed on tall buildings or on masts in order to achieve the best coverage possible. Whilst some masts have antennae that transmit in three directions (full 360 degrees), some may only transmit in one and produce limited directional coverage. The cell site analysis expert must therefore determine what type of mast has been used in order to collect the most reliable results possible during an investigation. Each antennae in use by a cell site will also have a unique reference that is recorded and included on mobile phone data records (with the exception of network O2 who reference cell sites but not individual antennae). These unique references form the basis for cell site analysis and confirm what mast was in use by a suspects mobile phone and when.
Although cell sites have the ability to transmit over large distances, signal quality can be less effective or entirely blocked by tall buildings, condensed objects and other obstructs. Users in these ‘black spots’ may experience a decrease in communications quality or a complete halt to mobile phone services. In these instances, a mobile phone could connect to another large cell site with better coverage or to smaller cell sites known as picocells, microcells and femtocells if one were available. Picocells, microcells and femtocells are placed in black spots and other difficult areas (such as train stations) in order to provide a good service that a large cell site cannot achieve. Although each provides a slightly different type of service, they all allow for basic mobile phone communication such as short message service (SMS) and conversations.
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