As many have pointed out, our mobile phones are the perfect surveillance device. Most people carry them around — voluntarily — while they are awake. Put this together with the fact that mobile phones have to connect to a nearby transmitter in order to work, and you end up with a pretty good idea of where the person using the device is throughout the day. No surprise, then, that police and prosecutors around the world turn routinely to phone tracking data when they are investigating cases. But as the New York Times reports, there can be serious problems with simply assuming the results are reliable. The Danish authorities have to review over 10,000 court verdicts because of errors in mobile phone tracking data that was offered as evidence in those cases. In addition, Denmark’s director of public prosecutions has ordered a two-month halt in the use of this location data in criminal cases while experts try to sort out the problems:
The first error was found in an I.T. system that converts phone companies’ raw data into evidence that the police and prosecutors can use to place a person at the scene of a crime. During the conversions, the system omitted some data, creating a less-detailed image of a cellphone’s whereabouts. The error was fixed in March after the national police discovered it.
In a second problem, some cellphone tracking data linked phones to the wrong cellphone towers, potentially connecting innocent people to crime scenes, said Jan Reckendorff, the director of public prosecutions.
It’s not clear yet how serious these blunders will turn out to be — it might only be a few, relatively minor cases. Or it might involve a large number of more serious crimes. Either way, it’s a salutary reminder that however useful a technology might appear for the purposes of solving crimes — and however straightforward its application seems — things can and will go wrong. There’s another approach that some people tend to view as infallible: the use of DNA sequencing techniques to identify suspects from material left at the scene of the crime. DNA is undoubtedly a powerful way of pulling information from tiny amounts of material, but there are a number of ways in which it can mislead badly. The same applies to mobile phone location data, as the Danish experience usefully underlines.