Phone-hacking trial: Cell phones and expert mistakes
- Court hears detailed "cell phone location evidence"
- Expert witness admits "error in his evidence"
- Defence statements not given to witness by police
Court resumed this morning to hear more evidence from forensic expert David Cutts on mobile telephone "cell site location" - evidence related to charge seven, an accusation of conspiracy to pervert the court of justice against Rebekah Brooks, her husband Charlie Brooks and former News International security chief Mark Hanna. The majority of this, the jury was told, is uncontested and shows the defendant's movements on the weekend Rebekah Brooks was first arrested over phone-hacking, between 15-17 July 2011. As the jury heard yesterday, mobile phone providers keep a record of which phone connects with which mast for billing purposes.
Evidence: The court heard about the logistics of phone masts
Over this weekend, the court was told, the Brookses were not at their usual Oxfordshire residence Jubilee Barn Farm, and instead were staying at another Oxfordshire location, Enstone Manor Farm, where they were being guarded by an "anti-intrusion" security team coordinated by Mark Hanna. On Sunday 17 July, Rebekah and Charlie Brooks were driven into London, with him going to their Chelsea flat while Rebekah Brooks attended an appointment at Lewisham police station. Events at the Chelsea flat that day were the subject of yesterday's evidence, .
Asked by Mark Bryant-Heron for the prosecution, Cutts gave a more detailed explanation of cell site location analysis. A powerpoint presentation was displayed on the court screens and the witness talked the court through it. A mobile telephone mast, he explained, is a "low powered localised radio transmitter" and the thousands of these in the country make up a series of "inter-connected cells". Each company records the date, time and length of the call and the IMEI number unique to every handset, as well as the address and postcode of the cell sites that handled the event. If someone is travelling, Cutts told the court, they may connect to a number of different cell towers during the course of a call.
Each telephone mast, Cutts explained, has three directional antenna each providing coverage to a third of the surrounding area. By looking at this data the witness said it is possible to deduce what "azimuth" the call originated from and draw a conclusion on which direction from the mast the phone was located. There are, he said, different types of cell sizes, smaller in urban areas, bigger in rural locations such as Oxfordshire where a cell size can be up to 8km around the mast.
The jury were then given a map showing to the area of contention, the movements of Mark Hanna and security contractor Lee Sandell on the morning of 17 July. It is agreed that both were at Enstone Farm that morning but did they, as the prosecution contend, later visit the Brooks' home address at Jubilee Barn? Cutts told the court he had visited the area and, although not granted access to the property, had done a survey to discover which mobile telephone masts served the local area. The witness told the court that, in his opinion, the data showed that both men's phones had been in the vicinity of Jubilee Barn between 9am and 10am that day.
The court then took a short break.
When the jury returned the forensic expert went into detail on his opinion, cross referencing calls made by Hanna and Sandell with the cell sites used. William Clegg, the defence QC for Hanna, then rose to cross-examine the witness. He asked the officer if he had been "careful" in his work as a "man's liberty is at stake", to which Cutt agreed. The counsel turned to the officer's statement and asked him to confirm that it contained a mistake as one of the calls listed could not have been made from Jubilee Barn. The witness said that this was "simply a mistake". Justice Saunders intervened and asked Cutts if he had not checked his evidence before taking the stand. Cutts replied that he had given a lot of evidence in the case and had just made an error.
Clegg then pointed to another phone call which was also mistakenly listed as being near Jubilee Barn. The witness explained that the farm had been given two different names during his survey and that had caused some "confusion in his data".
"This is a bit of a muddle" Clegg said. Cutts told the court it was a "human error". The QC put it to the witness that he was just "thrashing about and saying the first thing that came into his head". Clegg then turned to three calls on the billing records which he put to the witness could not have been made in the vicinity of Jubilee Barn. Clegg asked the officer: "Why does your statement say the opposite?" Cutts replied that this was also a mistake and was asked "are there any other mistakes?" The witnesss replied: "Not to my knowledge."
Clegg then postulated that, rather than the mobile phones being at Jubilee Barn itself, the cell phone data could have related to the road outside the property and suggested it could be consistent with someone driving past on the way to Chipping Norton. Cutts responded that he did not have the data one way or the other but agreed "it could have been possible". A map was shown to the court showing that the most direct route between Enstone farm and Chipping Norton did pass close to Jubilee Barn. The witness replied that this was not a possibility he had been asked to consider so he could not directly comment. Cutts said he usually asked for defence case statements so he could check their version of events but could not recall receiving that of Hanna outlining his version of events that day although he had asked for it. The defence QC said that Hanna's statement had been served 10 months ago but the witness could not assist the court on why he had never been given it to consider by the police.
The defence lawyer put it to the witness that the cell phone evidence was "more consistent" with the idea of a car passing Jubilee Barn than calls being made from the property itself. Cutts agreed that some it could be and after further detailed discussion over individual calls the court adjourned for lunch.
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