criminal offences, by lowering the requirements of foreseeability of the causal chain.
However, the legal basis for the interference must then also require a sufficiently
specified threat, in the sense that there be at least factual indications of the emergence of a specific threat to the legally protected interests. General experience alone
is not sufficient for justifying an interference. Rather, certain facts must be determined
that, in the individual case, substantiate the prognosis that an event leading to an imputable violation of the legally protected interests relevant here will occur (cf. BVerfGE 110, 33 <56 and 57, 61>; 113, 348 <377 and 378>). A sufficiently specific threat
in this sense may already exist even where the causal chain leading to the damage is
not yet foreseeable with sufficient probability, as long as certain facts already indicate
that a threat to an exceptionally significant legal interest may occur. In such a case,
the facts must allow the inference of, firstly, an occurrence that can be specified at
least with regard to its type and which is temporally foreseeable, and, secondly, of
the involvement of persons whose identity has at least been determined to the extent that the surveillance measure can target them specifically and is largely limited
to them (BVerfGE 120, 274 <328 and 329>; 125, 260 <330 and 331>). With regard to
terrorist offences, which are often committed at unforeseeable locations, planned far
in advance by individuals who have no criminal record, and carried out in very different ways, surveillance measures may also be authorised if, despite the lack of a temporally foreseeable occurrence of a specific type, the individual behaviour of a person
substantiates the specific probability that the person will commit such offences in the
near future. For instance, this is conceivable in the case of a person entering the Federal Republic of Germany after having been abroad at a training camp for terrorists.
In contrast, the weight of interference of covert police surveillance measures is not
sufficiently taken into account when the factual grounds for the interference are shifted so as to include the preliminary stages of a still vague and unforeseeable specific
threat to the legal interests protected by the provision. Linking the threshold for interference to the preliminary stages is constitutionally unacceptable if there are only relatively diffuse indications for potential threats, given the weight of the interference.
The factual situation at such a stage is often characterised by the rather ambivalent
meaning of individual observations. While occurrences may remain harmless, they
might also be part of a process that develops into a threat (cf. BVerfGE 120, 274
<329>; see also BVerfGE 110, 33 <59>; 113, 348 <377>). Such openness is not sufficient as a basis for carrying out covert and highly intrusive surveillance measures.
For example, the mere knowledge that a person is attracted to a fundamentalist understanding of religion would not be sufficient for such measures.
113
c) Tiered requirements arise with regard to the extent to which surveillance measures can be carried out in a target person’s sphere where the measures also affect
persons not responsible for particular actions or circumstances or who are not suspects and therefore bear no special responsibility.
114
Access to information technology systems and the surveillance of private homes
may only directly target persons responsible for impending or imminent dangers (cf.
115
15/71