received a call from a defense attorney on the east coast regarding a cellular forensics report he had received from the prosecution that concluded that the forensic cellular evidence proved his client was in the area of the scene of a crime at the time the crime was committed. The prosecutor had no physical evidence placing his client at the scene, and his client had an alibi corroborated by the client’s mother.
He requested our cellphone expert review the report. Cell phone tracking using cellular tower triangulation is not as simple as it initially looks. And because it looks like a simple identification process, the conclusions can be inaccurate and erroneous.
In order to accurately go about locating cellular locations, not only does the cell phone investigation have to take into account the tower locations, but also the antenna locations and direction. Terrence P. O’Connor explains in the Small Scale Digital Device Forensics Journal what happens:
“The tower and antenna which receives the call is determined by which antenna is receiving the signal from the mobile unit the strongest provided that tower is not already overloaded with call. When a tower is in a period of very high use it may switch the incoming call to an alternate tower and antenna provided that the mobile unit is in the alternate antenna’s field and therefore being received in adequate strength.”
Simply, cell phone forensics analysts should not assume that the tower the phone connects with is the closest tower to the phone and indicates proximity of the phone. The closest tower may be overloaded with calls and pushing signals to other towers.
The cell tower location, the antenna’s direction and field, azimuth pattern, terrain and usage load at a particular time and day all have to be taken into consideration to result in accurate cellular location evidence. Each call in the cell phone records, each tower and each antenna had to be analyzed and mapped, which is what was done.
The conclusion was that the prosecutor’s report was inaccurate. Because of the expertise of the team and the research behind the protocol, the investigator was able to testify about the process and provide accurate forensic cell tower evidence.
The accused was exonerated. The attorney was happy. His client was happy and was happy with another case closed.
-Brenda McGinley, CEO, All in Investigations, All in Investigations
