Diplomatic relations — Special missions — Status under customary international law — Inter-State agreements providing for immunity of special envoys — Conditions for effectiveness under customary international law — Requirement of specific task — United Nations Convention on Special Missions, 1969 — Whether embodying rules of customary international law

Diplomatic relations — Special missions — Conditions for establishment — Agreement between sending and receiving States — Requirement of specific task — Whether detailed description of tasks to be performed is required — Whether tacit agreement is sufficient

Diplomatic relations — Immunity — Special envoys — Immunity from criminal jurisdiction — Scope of immunity — Whether wider than immunity of members of diplomatic missions — Functional theory — Agreement to grant immunity ad personam ineffective under municipal law — Whether immunity may be established after entry of envoy into receiving State — Circumstances in which concept of abuse may prevent immunity from being recognized — Whether immunity extends until envoy leaves receiving State even if mission terminates earlier

Diplomatic relations — Immunity — Diplomats — Scope of immunity — Whether immunity gives rise to exemption from prosecution or merely constitutes a procedural bar — Circumstances in which envoy may be subject to prosecution upon cessation of functions — Vienna Convention on Diplomatic Relations, 1961, Article 39(2)

States — Conduct of foreign relations — Scope of judicial review — Inter-State agreement conferring immunity on special envoy — Whether subject to scrutiny by municipal courts

Sources of international law — General — State practice — Treaties — Writings of publicists — Evolution of customary international law — Diplomatic relations — Special missions

Relationship of international law and municipal law — Customary international law — Application by municipal courts — Rules of international law governing status and immunity of special envoys — Inter-State agreement concerning special envoy — Justiciability by municipal courts — The law of the Federal Republic of Germany