The provision permits surveillance outside of private homes using the means listed
in section 2. Among these, in particular, are surveillance for extended periods, the
covert creation of visual records, the covert monitoring of non-public speech, the application of tracking devices, or the use of police informants and undercover investigators.
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The weight of interference of these measures can vary greatly. It extends from
rather small to medium interferences, such as the taking of individual photographs or
simple observation for a limited time, all the way to serious interferences such as the
long-term on-going covert audio and visual recording of a person. Particularly when
these measures are carried out together and thereby aim, with the help of modern
technology, to register and audio-visually record as many utterances and movements
as possible, they can constitute a particularly serious interference with privacy.
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Similarly to the prevention of other weighty violations of legal interests or to the prosecution of significant criminal offences, the public interest in the effective prevention
of terrorism can justify such interferences (see above, C II 3 a), provided that they are
designed in a proportionate manner. This is, however, only partially the case here.
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c) Deriving from general security law, the conditions for interference set out in in
§ 20g sec. 1 no. 1, sec. 2 BKAG are not objectionable.
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aa) The provision limits the surveillance measures to the protection of sufficiently
weighty legal interests.
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Firstly, this applies insofar as it allows measures for the purpose of protecting the
existence or the security of the state or the life, limb, or freedom of persons. In addition, the same applies to the extent that the provision allows measures aiming at the
protection of property of substantial value the preservation of which is in the public interest. A reasonable interpretation of this will not include the preservation merely of
significant material assets. Rather, in the regulatory context of the protection against
terrorism, this will be taken to mean significant infrastructure facilities or other sites of
direct importance for society (vgl. BVerfGE 133, 277 <365 para. 203>).
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Pursuant to § 20g sec. 1 no. 1 BKAG, the powers to interfere are also further restricted in that measures for the protection of the legal interests mentioned above are
only permitted when these are threatened by one of the criminal offences listed in
§ 4a sec. 1 sentence 2 BKAG. This is evident in function provision of § 4a BKAG itself
into which the powers of §§ 20a et seq. BKAG are integrated. The powers to interfere
are thus restricted to the protection against threats from international terrorism. Here,
the legislature does not merely refer to the unspecific term “terrorism”, nor to §129
StGB in general, but rather it specifies that the threat to legal interests must emanate
from specific criminal offences that are individually defined and particularly qualified
in § 129a StGB. The provision is thus restricted to the protection of particularly
weighty legal interests against particularly threatening attacks. Leaving aside the
question of where the constitutional limits generally lie in respect of such measures –
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