In so far as diplomats are concerned, their immunity from legal process arises under customary international law and treaty law (i.e., the Vienna Convention on Diplomatic Relations,' the Vienna Convention on Consular Relations,2 and the New York Convention on Special Missions' (or "New York Convention")). All three conventions state in their preliminaries that diplomatic immunity and privilege arise from international custom and that their function is not to benefit individuals, but to ensure the smooth and efficient performance of their duties in the interest of comity and of friendly relations between sovereign nations.
The Function of State and Diplomatic Privileges and Immunities in International Cooperation in Criminal Matters: The Position in Switzerland,
23 Fordham Int'l L.J. 1334
Available at: https://ir.lawnet.fordham.edu/ilj/vol23/iss5/3