b) First of all, the right of a parliamentary committee of inquiry to collect evidence is
limited by the investigation mandate as defined by the decision establishing the committee. The investigation mandate as such must remain within the scope of the Parliament’s oversight powers, and it must be defined in a sufficiently clear manner (cf.
BVerfGE 124, 78 <118 and 119>).
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c) Moreover, reasons to withhold information from a committee of inquiry may arise
under the principle of separation of powers (cf. BVerfGE 124, 78 <120>; regarding
the limits of the right to information vested in the Bundestag as well as in its individual
Members, cf. BVerfGE 137, 185 <233 para. 135>).
117
The principle of separation of powers aims to ensure a division of power in order to
moderate the sovereign authority of the state. In its manifestation under the Basic
Law as a principle requiring that legislative, executive and judicial power be distinguished (Art. 20(2) second sentence GG), it also contributes to a functional and dutyoriented assignment of sovereign powers to different public authorities, each of which
is organised in a manner suited to their respective tasks; in addition, the principle ensures that all authority be bound by [the rule of] law (Art. 20(3) GG) (cf. BVerfGE 124,
78 <120>; 137, 185 <233 para. 135>). In the constitutional system of the Basic Law,
separation of powers is neither stipulated nor implemented in terms of an absolute
separation. The different branches of government are inter-related and intertwined,
yet they may not be deprived of their respective distinctiveness and their specific
tasks and competences (cf. BVerfGE 9, 268 <279 280>; established case-law).
Therefore, the principle of separation of powers provides both the basis and the limitation of Parliament’s right to information vis-à-vis the Federal Government (cf. BVerfGE 110, 199 <219>; 124, 78 <122>; 137, 185 <233 para. 135>).
118
aa) The responsibility of the Federal Government vis-à-vis Parliament and the people necessarily requires a core sphere of autonomous executive decision-making
(Kernbereich exekutiver Eigenverantwortung), which generally encompasses a
sphere relating to initiative, deliberation and action that is not open to investigation.
[…]
119
As a rule, a duty of the Federal Government to provide information requested by
Parliament does not exist where such information could result in a co-governing by
third parties of decisions that fall within the exclusive competence of the Federal Government. […]
120
[…]
121
bb) In light of the constitutional framework governing the assignment of public tasks
to specific public duties and responsible authorities, the responsibility of the Federal
Government vis-à-vis Parliament and the people requires an effective guarantee that
state functions be exercised in a duty-oriented manner and by the appropriate organ
(funktionsgerechte und organadäquate Aufgabenwahrnehmung).
122
(1) The Basic Law imposes a duty on all constitutional organs to avert impairments
123
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