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Danish data retention: Back to normal after major crisis

November 20, 2019 In Digital Freedom

The Danish police and the Ministry of Justice consider access to
electronic communications data to be a crucial tool for investigation
and prosecution of criminal offences. Legal requirements for blanket
data retention, which originally transposed the EU Data Retention
Directive, are still in place in Denmark, despite the judgments from the
Court of Justice of the European Union (CJEU) in 2014 and 2016 that
declared general and indiscriminate data retention illegal under EU law.

In March 2017, in the aftermath of the Tele2 judgment, the Danish
Minister of Justice informed the Parliament that it was necessary to
amend the Danish data retention law. However, when it comes to illegal
data retention, the political willingness to uphold the rule of law
seems to be low ? every year the revision is postponed by the Danish
government with consent from Parliament, citing various formal excuses.
Currently, the Danish government is officially hoping that the CJEU will
revise the jurisprudence of the Tele2 judgment in the new data retention
cases from Belgium, France and the United Kingdom which are expected to
be decided in May 2020. This latest postponement, announced on 1 October
2019, barely caught any media attention.

However, data retention has been almost constantly in the news for other
reasons since 17 June 2019 when it was revealed to the public that
flawed electronic communications data had been used as evidence in up to
10000 police investigations and criminal trials since 2012. Quickly
dubbed the ?telecommunications data scandal? by the media, the
ramifications of the case have revealed severely inadequate data
management practices by the Danish police for almost ten years. This is
obviously very concerning for the functioning of the criminal justice
system and the right to a fair trial, but also rather surprising in
light of the consistent official position of the Danish police that
access to telecommunications data is a crucial tool for investigation of
criminal offences. The mismatch between the public claims of access to
telecommunications data being crucial, and the attention devoted to
proper data management, could hardly be any bigger.

According to the initial reports in June 2019, the flawed data was
caused by an IT system used by the Danish police to convert
telecommunications data from different mobile service providers to a
common format. Apparently, the IT system sometimes discarded parts of
the data received from mobile service providers. During the Summer of
2019, a new source of error was identified. In some cases, the data
conversion system had modified the geolocation position of mobile towers
by up to 200 meters.

Based on the new information of involuntary evidence tampering, the
Director of Public Prosecutions decided on 18 August 2019 to impose a
temporary two-month ban on the use of telecommunications data as
evidence in criminal trials and pre-trial detention cases. Somewhat
inconsequential, the police could still use the potentially flawed data
for investigative purposes. Since telecommunications data are frequently
used in criminal trials in Denmark, for example as evidence that the
indicted person was in the vicinity of the crime scene, the two-month
moratorium caused a number of criminal trials to be postponed.
Furthermore, about 30 persons were released from pre-trial detention,
something that generated media attention even outside Denmark.

In late August 2019, the Danish National Police commissioned the
consultancy firm Deloitte to conduct an external investigation of its
handling of telecommunications data and to provide recommendations for
improving the data management practices. The report from Deloitte was
published on 3 October 2019, together with statements from the Danish
National Police, the Director of Public Prosecutions, and the Ministry
of Justice.

The first part of the report identifies the main technical and
organisational causes for the flawed data. The IT system used for
converting telecommunications data to a common format contained a timer
which sometimes submitted the converted data to the police investigator
before the conversion job was completed. This explains, at least at
technical level, why parts of the data received from mobile service
providers were sometimes discarded. The timer error mainly affected
large data sets, such as mobile tower dumps (information about all
mobile devices in a certain geographical area and time period) and
access to historical location data for individual subscribers.

The flaws in the geolocation information for mobile towers that
triggered the August moratorium were traced to errors in the conversion
of geographical coordinates. Mobile service providers in Denmark use two
different systems for geographical coordinates, and the police uses a
third system internally. During a short period in 2016, the conversion
algorithm was applied twice to some mobile tower data, which moved the
geolocation positions by a couple of hundred meters.

On the face of it, these errors in the IT system should be relatively
straightforward to correct, but the Deloitte report also identifies more
fundamental deficiencies in the police practices of handling
telecommunications data. In short, the report describes the IT systems
and the associated IT infrastructure as complex, outdated, and difficult
to maintain. The IT system used for converting telecommunications data
was developed internally by the police and maintained by a single
employee. Before December 2018, there were no administrative practices
for quality control of the data conversion system, not even simple
checks to ensure that the entire data set received from mobile service
providers had been properly converted.

The only viable solution for the Danish police, according to the
assessment in the report, is to develop an entirely new infrastructure
for handling telecommunications data. Deloitte recommends that the new
infrastructure should be based on standard software elements which are
accepted globally, rather than internally developed systems which cannot
be verified. Concretely, the reports suggests using POL-INTEL, a big
data policing system supplied by Palantir Technologies, for the new IT
infrastructure. In the short term, some investment in the existing
infrastructure will be necessary in order to improve the stability of
the legacy IT systems and reduce the risk of creating new data flaws.
Finally, the report recommends systematic independent quality control
and data validation by an external vendor. The Danish National Police
has accepted all recommendations in the report.

Deloitte also delivered a short briefing note about the use of
telecommunications data in criminal cases. The briefing note, intended
for police investigators, prosecutors, defence lawyers and judges,
explains the basic use cases of telecommunications data in police
investigations, as well as information about how the data is generated
in mobile networks. The possible uncertainties and limitations of
telecommunications data are also mentioned. For example, it is pointed
out that mobile devices do not necessarily connect to the nearest mobile
tower, so it cannot simply be assumed that the user of the device is
close to the mobile tower with almost ?GPS level? accuracy. This
addresses a frequent critique against the police and prosecutors for
overstating the accuracy of mobile location data ? an issue that was
covered in depth by the newspaper Information in a series of articles in
2015. Quite interestingly, the briefing note also mentions the
possibility of spoofing telephone numbers, so that the incoming
telephone call or text message may originate from a different source
than the telephone number registered by the mobile service provider
under its data retention obligation.

On 16 October 2019, the Director of Public Prosecutions decided not to
extend the moratorium on the use of telecommunications data. Along with
this decision, the Director issued new and more specific instructions
for prosecutors regarding the use of telecommunications data. The
Deloitte briefing note should be part of the criminal case (and
distributed to the defence lawyer), and police investigators are
required to present a quality control report to prosecutors with an
assessment of possible sources of error and uncertainty in the
interpretation of the telecommunications data used in the case.
Documentation of telecommunications data evidence should, to the extent
possible, be based on the raw data received from mobile service
providers and not the converted data.

For law enforcement, the October 16 decision marks the end of the data
retention crisis which erupted in public four months earlier. However,
only the most imminent problems at the technical level have really been
addressed, and several of the underlying causes of the crisis are still
looming under the surface, for example the severely inadequate IT
infrastructure used by the Danish police for handling telecommunications
data. The Minister of Justice has announced further initiatives,
including investment in new IT systems, organisational changes to
improve the focus on data management, improved training for police
investigators in the proper use and interpretation of telecommunications
data, and the creation of a new independent supervisory authority for
technical investigation methods used by the police.

Denmark: Our data retention law is illegal, but we keep it for now
(08.03.2017)
https://edri.org/denmark-our-data-retention-law-is-illegal-but-we-keep-it-for-now/

Denmark frees 32 inmates over flaws in phone geolocation evidence, The
Guardian (12.09.2019)
https://www.theguardian.com/world/2019/sep/12/denmark-frees-32-inmates-over-flawed-geolocation-revelations

Response from the Minister of Justice to the reports on
telecommunications data (in Danish only, 03.10.2019)
http://www.justitsministeriet.dk/nyt-og-presse/pressemeddelelser/2019/justitsministerens-reaktion-paa-teledata-redegoerelser

Can cell tower data be trusted as evidence? Blog post by the journalist
covering telecommunications data for the newspaper Information (26.09.2015)
https://andreas-rasmussen.dk/2015/09/26/can-cell-tower-data-be-trusted-as-evidence/

(Contribution by Jesper Lund, EDRi member IT-pol, Denmark)