Ian Huntley's conviction for the murder of Holly Wells and Jessica Chapman was based partly on crucial mobile phone evidence - which nowadays is almost as useful to the police as fingerprints or DNA.
By Chris Summers
BBC News Online
Huntley was knowledgeable about some aspects of forensic science - such as analysis of fibres - but it was his ignorance about mobile phones that proved his undoing.
Jessica's mobile logged on to a mast at Burwell
He was not alone in being unaware of how powerful evidence from cellular phone networks could be when it comes to proving where somebody was at a key moment.
In the past five years, dozens of murderers have been convicted partly as a result of evidence about their mobile phones or those of their victims.
Detectives now routinely contact the mobile phone networks and obtain details of phone calls made by and to a murder victim and from the prime suspects.
Trials featuring mobile phone evidence
Stuart Campbell (Dec 2002): Convicted of murdering Danielle Jones
Colm Murphy (Jan 2002): Convicted of Omagh bomb plot
Two juveniles (Apr 2002): Acquitted of murdering Damilola Taylor
Senthamil Thillainathan (Jun 2003): Convicted, along with two others, of killing a Tamil youth
Jack Whomes and Mick Steele (Jan 1998): Convicted of murdering three gangsters in Essex (but seeking appeal based on new mobile phone evidence)
The response varies from network to network.
David Bristowe, the prosecution's expert witness on mobile phones at the Soham trial, believes companies should be forced to keep the data longer.
"The data should be kept for at least two years because you never know how a case is going to develop and when you might need to trace somebody's calls."
Jack Wraith, of the Mobile Phone Industry Crime Action Forum, which represents the networks, said there was a conflict between public interest and the Data Protection Act.
He said: "There have been moves under the Terrorism Act to make us retain data for longer but the networks said to the Home Office: 'If you want us to keep this data you must legislate, otherwise we will not be covered by the law and could be sued'."
Only one point on the girls' route was served by Burwell - Huntley's house
Most organised criminals are aware of the dangers of being tracked by their mobiles. Professional drug dealers and armed robbers will often buy pay-as-you-go phones a few days before they plan a crime and dispose of them straight afterwards.
Mr Bristowe told BBC News Online: "It was mobile phone evidence which made the police look more closely at Huntley.
"He had been Mr Useful, helping them to search the college grounds, but when they checked Jessica's phone and discovered when and where it had been switched off alarm bells began to ring."
He said: "The evidence against Huntley was simple.
"There were two aspects. One was 'where was Jessica's phone when it turned off?' and the other was 'where was Huntley's phone a couple of days later when he changed tyres on his car in Ely?'."
Mr Bristowe told the trial Jessica's phone "disengaged itself from the network, in effect it says goodbye" at 1846BST on the Sunday when the girls disappeared.
He told the jury that when mobile phones are switched off they go through a process which is recorded by the cell site mast providing the last signal.
Mobile phone evidence helped convict Stuart Campbell of murdering Danielle Jones
Although a cell site mast at Soham football club served most of the village there were several small "hot spots" which instead linked to a mast at Burwell several miles away.
Jessica's phone contacted the Burwell mast when it was turned off.
Mr Bristowe told BBC News Online: "The police provided us with a map of the route they thought the girls would have taken, and the only place on that route where the phone could have logged on to Burwell was inside or just outside Huntley's house."
It is believed to be that crumb of crucial evidence which forced Huntley to change his story earlier this year and suddenly admit the girls died in his bathroom albeit in bizarre circumstances.
Huntley, faced with the phone evidence about Ely, also admitted he had changed the tyres on his car a day after dumping the bodies.
But while mobile phone evidence is routinely used by the police when seeking evidence to link people to crimes it may also be a useful tool for those trying to clear their names.
In the 1990s juries were shown complex cell site maps such as this one
In 1998 Jack Whomes and Mick Steele were jailed for life for the murder of three Essex gangsters, who were found shot dead in a Range Rover parked in a quiet lane near the village of Rettendon.
The jury were given complex evidence about mobile phones which, the prosecution claimed, placed Whomes at the scene of the crime on the night of the killings.
A supergrass, Darren Nicholls, who claimed to have been the getaway driver, told the trial Whomes had phoned him from the lane after the killings.
But Mr Bristowe has since returned to Workhouse Lane in Rettendon and carried out extensive tests using Whomes' own mobile.
He made about 60 calls at various places in the lane, and not one of those calls was routed through the cell site at a place called Hockley, as the prosecution had claimed.
Jack Whomes is hoping new tests on his mobile phone will prove his innocence
Mr Bristowe said his tests supported Whomes' own version of events - that he was more than a mile away picking up Nicholls' broken down car.
He also believes the phone evidence was lost on the jury at the 1998 trial because it was so complex.
Whomes and Steele are hoping to find out in January if their case has been referred back to the Court of Appeal by the Criminal Cases Review Commission.