account that it is not possible to reduce the generation of knowledge – and not least
when aiming to understand terrorist structures – to a mere sum of separated and individual data which one could reveal or suppress in line with legal criteria. Within the
described limits, this is recognised by the legal order. […]
Observance of the principle of purpose limitation depends on whether the authority
that is empowered to collect data uses it while acting within the same assignment of
tasks for the protection of the same legal interests and the prosecution or prevention
of the same criminal offences as is determined in the relevant data collection provision. These requirements are necessary but generally also sufficient to legitimise a
further use of the data within the scope of the principle of purpose limitation.
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However, with regard to data obtained by means of the surveillance of private
homes and remote searches, the principle of purpose limitation is broader in scope:
here, any further use of the data only correlates with the purpose if it is also necessary in accordance with the collection requirements of a corresponding imminent danger (cf. BVerfGE 109, 279 <377, 379>) or a specific impending danger (cf. BVerfGE
120, 274 <326, 328 and 329>). The extraordinary weight of the interference resulting
from such data collection is also reflected in a particularly narrow limitation of any further use of the obtained data to the requirements and thus to the purposes of the data
collection.These findings may not be used as a mere evidentiary basis for further investigations irrespective of an imminent or specific impending danger.
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2. The legislature may also allow for a further use of data for other purposes than
those determining the original data collection (change in purpose). In that case, however, the legislature must ensure that the weight of the interference resulting from the
data collection is also taken into consideration with regard to the new use of data (cf.
BVerfGE 100, 313 <389 and 390>; 109, 279 <377>; 120, 351 <369>; 130, 1 <33 and
34>; 133, 277 <372 and 373 para. 225>).
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a) The authorisation to use data for new purposes constitutes a new interference
with the fundamental right with which the data collection interfered (cf. BVerfGE 100,
313 <360, 391>; 109, 279 <375>; 110, 33 <68 and 69>; 125, 260 <312 and 313,
333>; 133, 277 <372 para. 225>; cf. also ECtHR, Weber and Saravia v. Germany,
judgment of 29 June 2006, no. 54934/00, para. 79, NJW 2007, p. 1433 <1434>, on
Art. 8 ECHR). For that reason, changes in purpose need to be measured against
those fundamental rights that were relevant for the data collection. This applies to any
type of data use for purposes differing from those for which the data was originally
collected, irrespective of whether the use pursues evidential purposes or constitutes
a mere evidentiary basis for further investigations (cf. BVerfGE 109, 279 <377>).
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b) In that respect, an authorisation to change the purpose is subject to the principle
of proportionality. The weight attached to such a provision when weighing considerations corresponds to the weight of the interference resulting from the data collection.
Information obtained by measures constituting a serious interference may only be
used for particularly weighty reasons (cf. BVerfGE 100, 313 <394>; 109, 279 <377>;
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