Denmark has released 32 prisoners as part of an ongoing review of 10,700 criminal cases after serious questions arose about the reliability of geolocation data obtained from mobile phone operators, local media have reported.
Nearly 40 new cases have been postponed under a two-month moratorium on the use of mobile phone records in trials, which was imposed after police found multiple glitches in the software that converts raw data from phone masts into usable evidence.
Among the errors police have discovered is a tendency for the system to omit some data during the conversion process, meaning only selected calls are registered and the picture of the phone’s location is materially incomplete.
The system has also linked phones to the wrong masts, connected them to several towers at once, sometimes hundreds of kilometres apart, recorded the origins of text messages incorrectly and got the location of specific towers wrong.
Taken together, the problems meant not just that innocent people could potentially have been placed at crime scenes but that criminals could have been wrongly excluded from inquiries, said Jan Reckendorff, Denmark’s director of public prosecutions.
“This is a very, very serious issue,” he told Denmark’s state broadcaster DR. “We simply cannot live with the idea that information that isn’t accurate could send people to prison.”
Announcing the case review and moratorium late last month, Reckendorff conceded it was a “drastic decision, but necessary in a state of law”.
The Danish justice minister, Nick Haekkerup, welcomed the decision, saying the first priority must always be to avoid miscarriages of justice. “We shouldn’t take the risk that innocent people could be convicted,” he said.
Operators insist the errors have mostly stemmed from the interpretation of their data and they should not be held responsible. Authorities contend that in some instances the data has also been at fault, but Jakob Willer, of the country’s telecoms industry association, said it was not their job to provide evidence.
“We should remember: data is created to help deliver telecom services, not to control citizens or for surveillance,” Willer said. He conceded it could be valuable to police, but insisted its primary purpose was to facilitate communication between users.
There are no statistics on how many court cases in Denmark are decided on the basis of mobile phone data, but it often used to corroborate other evidence and, although not considered as reliable as DNA, has previously been seen as highly accurate.
Karoline Normann, the head of the Danish law society’s criminal law committee, said evidence once considered purely technical was now open to doubt. “Until now, mobile data has had a high significance and value in courtrooms because this kind of evidence has been considered almost objective,” she told Agence-France Presse.
“This situation has changed our mindset about cellphone data. We are probably going to question it as we normally question a witness or other types of evidence, where we consider circumstances like who produced the evidence, and why and how.”
Isolated incidences of clearly inaccurate mobile data have occurred in the past in the US and South Africa, but this is the first time it has been questioned by a national justice system. Three years ago a Kansas family sued a digital mapping company after being visited “countless times” by police.
Rather than wait for their case to be examined under the review, Danish prisoners have started demanding their release on the grounds that their convictions were based on mobile phone evidence.
Not all are successful. Two members of an an Aarhus criminal gang – one of whom insisted he had spent the night at his parents’ home but was placed at a crime scene by mobile phone records – had their appeals turned down this week because other evidence was considered conclusive.