Can the security staff (equivalent to the U.S. Diplomatic Security Service) of the various Embassies/Missions/Consulates/etc located in New York City carry (concealed) firearms as part of their official duties providing security for their diplomatic staff while not on embassy grounds? Have these rules changed any since the 1960's?
Diplomatic and Consular Immunity: Guidance for Law Enforcement and Judicial Authorities explains the extent to which persons with diplomatic immunity are not subjects to the laws of the US:
Personal Inviolability vs. Public Safety Personal inviolability is enjoyed to some degree by a majority of foreign diplomatic and consular personnel. This inviolability generally precludes handcuffing, arrest, or detention in any form and forbids U.S. authorities from entering the residences, automobiles, or other property of protected persons. Personal inviolability is, however, qualified by the understanding, well established in international practice, that the host country does not give up its right to protect the safety and welfare of its populace and retains the right, in extraordinary circumstances, to prevent the commission of a crime. Thus, in circumstances where public safety is in imminent danger or it is apparent that a grave crime may otherwise be committed, police authorities may intervene to the extent necessary to halt such activity. This naturally includes the power of the police to defend themselves from personal harm.
So law enforcement can stop a shooting in progress, but they cannot arrest a person with immunity if they arrive at the scene of the shooting after the crime has taken place. If a person with immunity carries a holstered gun and presents credentials demonstrating immunity, they cannot be questioned any further unless they acquiesce to the questioning.
A license is required, see NYC Administrative Code §10-301. This page describes the procedure: the license type is presumably a "carry guard license". You must also get a New York State pistol license. There are various training requirements. Title 38 of the Rules of the City of New York ch. 5 (handgun licenses) says what the police department rules are for licensing, §5-04 describes the Carry Guard License, which basically says you must show the need to be armed and that you have any required licenses. If you can do this, they may issue you a license. You cannot carry a concealed firearm off the job just because you are consular security staff.
Vienna Convention on Consular Relations, April 24, 1963 21 U.S.T. 77 596 U.N.T.S. 261 Article 31:
"A diplomatic agent shall enjoy immunity from the criminal jurisdiction of the receiving State."123
End of story.
1 "He shall also enjoy immunity from its civil and administrative jurisdiction, except in [cases irrelevant herein]”
2 It became the "supreme [l]aw of the [l]and" under Article IV, section 2, of the U.S. Constitution after congress ratified it in 1973 without further action required on the part of any States.
3 No objections raised relating to the immunities provided by Article 31 by any of the high party signors, assentors, or ratifiers.