The key difference between a treaty and a convention is as follows:

Treaty:

A treaty is a formally concluded and ratified agreement between States. The term is used generically to refer to instruments binding at international law, concluded between international entities (States or organizations). Under the Vienna Conventions on the Law of Treaties [1], a treaty must be (1) a binding instrument, which means that the contracting parties intended to create legal rights and duties; (2) concluded by states or international organizations with treaty-making power; (3) governed by international law and (4) in writing. A treaty may be of two types that is a law making treaty, that may also be called as a convention and a contractual treaty.

Convention: A convention is a formal agreement between States. The generic term 'convention' is thus synonymous with the generic term 'treaty'. Conventions are normally open for participation by the international community as a whole, or by a large number of States. Usually the instruments negotiated under the auspices of an international organization are entitled conventions (e.g. the Convention on the Rights of the Child, adopted by the General Assembly of the United Nations in 1989).[2]

The Vienna Convention on Diplomatic relations (VCDR) [3] is a part of the group of Treaties and convention that were signed and ratified in Vienna, the capital of Austria and joins the Vienna Convention on Law of Treaties, Vienna convention on Consular Relations and Vienna Convention on Civil Liability for Nuclear Damage. Treaties form a part of a direct source of law under the article 38(1)(a) of the Statue of the International Court of Justice.[4]

The Vienna Convention on Diplomatic Relations (VCDR) of 1961(18 April 1961) is an international treaty that defines a framework for diplomatic relations between independent countries. It specifies the privileges of a diplomatic mission that enable diplomats to perform their function without fear of coercion or harassment by the host country. This forms the legal basis for diplomatic immunity. Its articles are considered a cornerstone of modern international relations. As of October 2018, it has been ratified by 192 states.

The Preamble of the VCDR very briefly gives us a description about the object of this treaty, where the parties to this treaty Recalls the position of the diplomatic officers and relations between countries through them and respect the same, having in mind the object of the United Nations that is the promotion and maintenance of international peace and security, believing that this treaty will bring about a positive attitude and relations between international state actors as respecting the diplomatic officers is respecting the sovereignty of the respecting country from which the diplomatic officer is from, the state actors realize that this convention and the immunities construed through this convention is for the benefit of the sovereign state actors and the diplomatic missions and not the individuals that act in the diplomatic capacity, and also creates a proviso that the rules that are not governed by this convention expressedly, will be governed by the rules of Customary International Law, which is also considered as a source of law under the article 38(1)(b) of the Statue of the International Court of Justice.

Article 1 of the VCDR defines certain terms that are used in the convention throughout, article 1(e) talks about a diplomatic agent is the head of the mission or a member of the diplomatic staff of the mission, however, this definition doesn't exactly define a diplomatic agent per se but gives two other terms to define the same however, the same has been defined in the same article, which is enshrined under article 1(a) as the head of the mission is the person charged by the sending State with the duty of acting in that capacity and also under article 1 (d) the members of the diplomatic staff are the members of the staff of the mission having diplomatic rank the members of the staff of the mission are defined under clause (c) as the members of the staff of the mission are the members of the diplomatic staff, of the administrative and technical staff and of the service staff of the mission.

Article 2 of the VCDR talks about that the diplomatic relations to be only by the consent of both the parties. Article 3 of this convention talks about the functions and purposes of a diplomatic officer. Article 4, however, gives power to the receiving state to stop an entry of a diplomatic agent into its sovereign limit, and is not obligated to give any reason for such denial. Article 6 permits the sending state and any other state to collaborate and send one diplomatic agent for both the states, unless it is objected by the receiving state. Article 8 makes it compulsory for the diplomatic agent to be a national of the sending state only, or if otherwise, there is consent received from the receiving state, itself.

Article 9 clause 1 talks about the latin term , which is persona non grata which, when translated in english roughly means person who is not welcome in the sovereign territory of the particular country, the decision to declare the same is with the receiving state and the same can be declared while the diplomatic officer is in the state or before he is sent with the diplomatic status, without explaining any reason, however the same has to be notified to the sending state, following this notification the sending state may recall the diplomatic agent who has been declared persona no grata or terminate his functions.

The clause 2 of the same article states that if the sending state doesn't fulfil its obligation that is enshrined in the clause 1 the receiving state has no obligation to treat him the same way as the Vienna convention on the law of treaties state as pacta sunt servanda (article 26)[5]. however, the person who is declared as persona non grata can still the enter the said territory as private person. Example of the same is Kurt Waldheim, former Secretary-General of the United Nations and President of Austria, and his wife were given persona non grata status in the United States and other countries when he was accused of having known about Nazi war crimes and not having done anything about them.[6]

Article 11,12,13 of the VCDR talk about the notification of the travel and other related information of the diplomatic agent dos and don'ts of the agent and the sending state.

Article 14 talks division of the agents into various classes, which are as follows:

1. that of ambassadors or nuncios accredited to Heads of State, and other heads of mission of equivalent rank}
2. that of envoys, ministers and internuncios accredited to Heads of State;
3. that of charges d'affaires accredited to Ministers for Foreign Affairs.

however, article 15 makes it clear that such classification, will be on the approval of both the states.

Article 19 states that if the position of the head of the mission is vacant then the person of a rank below or the charges d'affaires may take his position. article 21 makes it an obligation of the receiving state to provide for basic amenities to the diplomatic agent, and article 22 also makes it sure that the diplomatic office of the sending state shall be free from all the disturbances of the receiving state and shall be allowed to work in peace. while article 23 exempts the agent and office from taxes, article 24 states that the archives and documents of such mission shall not be accessible by the receiving state.

In accordance with Article 27(3) of the Vienna Convention on Diplomatic Relations (VCDR), properly designated diplomatic pouches shall not be opened or detained. A diplomatic pouch (or bag) is any properly identified and sealed package, pouch, envelope, bag, or other container that is used to transport official correspondence, documents, and other articles intended for official use, between:

• Embassies, legations, consular posts, and the foreign office of any government;
• The headquarters or any other office of a public international organization and its regional offices in the United States or in a foreign country; or
• The foreign office of any country with full membership in a public international organization and its mission to that organization[7]

Article 29,30,31,37 talks about the immunity from the arrest and detention of a diplomatic agent and their families in all criminal cases and civil and administrative cases , except in the cases of:

1. a real action relating to private immovable property situated in the territory of the receiving State, unless he holds it on behalf of the sending State for the purposes of the mission;
2. an action relating to succession in which the diplomatic agent is involved as executor, administrator, heir or legatee as a private person and not on behalf of the sending State
3. an action relating to any professional or commercial activity exercised by the diplomatic agent in the receiving State outside his official functions.

The agent may also not be asked to be a witness and the agent is not entitled to immunity from the sending state.

In the case of Criminal cases, A diplomatic agent can enjoy immunity ratione personae, if the person is a state official and the act(s) committed by the person are State Functions (immunity ratione materiae; article 38 of VCDR). Dealing with them one by one:
As per Customary International Law, immunity ratione personae to incumbent Ministers of Foreign Affairs to ensure the effective performance of their function on behalf of their respective States.[8]

Former Heads of State [9] and military commanders[10] are entitled immunity ratione materiae only in relation to their official acts done during the term of their office. In contrast to immunity ratione personae which is absolute, immunity ratione materiae is limited and covers only official acts [11] and acts which violate jus cogens norms do not qualify as sovereign acts.[12]

It is argued that whilst international crimes can be official acts, immunity ratione materiae is removed as soon as a rule permitting the exercise of extra-territorial jurisdiction over that crime and contemplating prosecution of state officials develops.[13] It has been well established by the lotus case [14] that where there is no jurisdiction of a domestic court to try an offense that court might not adjudicate upon that issue, according to the arrest warrant case[15], As per Customary International Law, immunity ratione personae to incumbent Ministers of Foreign Affairs to ensure the effective performance of their function on behalf of their respective States[16], the diplomatic immunity that Ms, Darian Grey enjoys, cannot be set aside, the same has also been put forward by the cases of Djibouti v. France[17] and United States of America v. Iran[18].

It has also been stated The 1973 Convention on the Prevention and Punishment of Crimes against Internationally Protected Persons, which also states that the diplomatic agents or representatives of states enjoys immunity.

Similarly, immunity ratione materiae is not a bar to the prosecution of crimes amounting to concerning war crimes and crimes against humanity because such acts are considered international crimes.[19]It has been also been established as a fact by the international criminal court that high level officials can be convicted for crimes committed internationally.[20] An international arrest warrant was also issued in the case concerning The President of Sudan, Mr. Omar Hassan Ahmad Al Bashir by the International Criminal Court for genocide, crimes against humanity and war crimes, therefore, showing that the same can happen in the such crimes and the international arrest warrant can be issued against the head of states[21].

The purpose of such privileges and immunities is not to benefit individuals but to ensure the efficient performance of the functions of diplomatic missions as representing States[22] as enshrined in the article 41 of VCDR , exceptions to the rule of immunity of the diplomatic agent are as follows:
Under Customary International Law, universal jurisdiction[23]entitles each and every state to have jurisdiction and try the offense.[24]It comes to use whenever there is a commission of crimes that are specifically offensive to an international community as a whole, such as torture[25] which, as is our case. As a probable cause does exist for the charge of torture[26] against the abovementioned.

The exercising of jurisdiction over persons whose acts are directed against the vital interests of the state, the fact that they're committed abroad doesn't affect it as such, is justified by the protective principle abroad.[27]To explain ,When Israel exercised jurisdiction to prosecute Eichmann due to its vital interests being in danger by Eichmann's order to kill all the Jewish citizens of Israel.[28] In Re Urios,[29]a Spanish National was convicted while he was in Spain during the First World War by the French authorities for espionage.

A State may exercise criminal jurisdiction over someone for his acts that are harmful to its nationals.[30]Applying this principle in U.S. v. Yunis, where several American nationals were on a flight that was hijacked, the Court held that the passive personality principle is an appropriate basis for jurisdiction.

For a receiving state to prosecute a diplomatic agent of his crimes, the sending state may deliver a expressed waiver of immunity to the receiving state as per article 32 of the VCDR.
The rest of the articles in the convention is an extension to the articles that are already stated above.

Therefore, the Vienna Convention On Diplomatic Relation helps states to ensure friendly and peaceful relations and makes sure that the work of these sovereign states are never stopped and there is peaceful flow of work and diplomacy throughout.

End-Notes:

1. Vienna Convention On The Law Of Treaties
2. https://www.unicef.org/french/crc/files/Definitions.pdf
3. https://treaties.un.org/doc/Treaties/1964/06/19640624%2002-10%20AM/Ch_III_3p.pdf
4. Statue of The International Court Of Justice Article 38:
   1. The Court, whose function is to decide in accordance with international law such disputes as are submitted to it, shall apply:
   
   1. international conventions, whether general or particular, establishing rules expressly recognized by the contesting states;
   2. international custom, as evidence of a general practice accepted as law;
5. Vienna Convention On The Law Of Treaties Article 26. Pacta Sunt Servanda; Every treaty in force is binding upon the parties to it and must be performed by them in good faith. Article 27. Internal Law And Observance Of Treaties A party may not invoke the provisions of its internal law as justification for its failure to perform a treaty. This rule is without prejudice to article 46.
6. https://www.nytimes.com/1986/07/09/opinion/waldheim-can-be-kept-out-of-the-us.html
7. https://www.state.gov/diplomatic-pouches/
8. Arrest Warrant, 2002 I.C.J. at ¶54; Dixon & Mccorquodale, Cases And Materials On International Law 318-319 (2003).
9. Bow Street, 2 All E.R. at 97; BROWNLIE, supra note 1, at 575
10. Bow Street, 2 All E.R. at 97.
11. Ibid
12. Prefecture of Voiotia v. Germany, Case no. 11/2000 (Greece: Supreme Court, 2000)
13. European Journal of International Law, Vol. 21
14. S.S. Lotus;, France v Turkey, Judgment, (1927) PCIJ Series A no 10
15. Case Concerning the Arrest Warrant of 11 April 2000 (Democratic Republic of Congo v. Belgium), [2002] I.C.J. Rep. 3 at 43-44 (Guillaume, President, Separate Opinion) [Arrest Warrant Case].
16. Arrest Warrant, 2002 I.C.J. at ¶54; DIXON & MCCORQUODALE, CASES AND MATERIALS ON
    INTERNATIONAL LAW 318-319 (2003).
17. Certain Questions of Mutual Assistance in Criminal Matters (Djibouti v. France), Judgment, I.C.J. Reports 2008, p. 177.
18. United States Diplomatic and Consular Staff in Tehran (United States of America v. Iran), Judgment, 24 May 1980
19. Prosecutor v. Blaskic, Case No.IT-95-14-T, at ¶41 (2000); Furundžija, Case No.IT-95-17/1- T, at ¶140; CASSESE, INTERNATIONAL CRIMINAL LAW 267 (2003).
20. United Nations Department of Public Information DPI/2016--October 1998, http://legal.un.org/icc/statute/iccq&a.htm.
21. THE PROSECUTOR v. OMAR HASSAN AHMAD AL BASHIR (OMAR AL BASHIR;), ICC-02/05-01/09-1.
22. preamble of the Vienna Convention on Diplomatic Relations, 1961(para 4).
23. CAT, Arts.4, 5, 9; R v. Bow Street Metropolitan Stipendiary Magistrate, ex parte Pinochet Ugarte, 2 All E.R. 97 (1999).
24. SHAW, supra note 3, at 592
25. Id. at 593
26. See discussion supra Part II(B).
27. Harvard Research, Draft Convention on Jurisdiction with Respect to Crime, 29 A.J.I.L. SUPP. 480, 519 (1935); United States v. Yunis, 681 F.Supp. 896 (1988)
28. Eichmann, 36 I.L.R. at 2
29. 1 A.D. 107 (1920).
30. CAT, art.5(1)(c); BANTEKAS & NASH, Arrest Warrant of April 11, 2000. Democratic Republic of Congo v. Belg.), 2002 I.C.J. 3, ¶¶16, 47.
    
     Written By: Abhishek Taneja, A student of amity Law school, Delhi