القاعدة ذات الصلة
United States of America
Practice Relating to Rule 161. International Cooperation in Criminal Proceedings
Section A. Cooperation between States
In 1979, in a diplomatic note addressed to the USSR embassy, the US Department of State stated:
The Department of State requests the cooperation of the Embassy of the USSR in bringing to the attention of the appropriate officials and organs the essential need for … witnesses to testify in the prosecution of war crimes cases in the United States. Without firm assurances on the availability of witnesses the United States Government will be unable to continue these prosecutions. In many cases, therefore, individuals accused of committing serious crimes during 1941–1945 will be allowed to remain free without a proper trial.
We believe that it is in the mutual best interest of the United States and the Union of Soviet Socialist Republics to cooperate to ensure that this result is avoided and that justice is done in these cases. 
United States, Department of State, Note addressed to the USSR Embassy, 21 March 1979, Department of State File No. P79 0046-0132, reprinted in Marian Lloyd Nash, Digest of United States Practice in International Law, 1979, US Department of State Publication 9374, Washington, D.C., 1983, pp. 883–884.
In 1987, the Deputy Legal Adviser of the US Department of State, referring to Articles 85–89 of the 1977 Additional Protocol I, affirmed: “We support the principle that the appropriate authorities … make good faith efforts to cooperate with one another.” 
United States, Remarks of Michael J. Matheson, Deputy Legal Adviser, US Department of State, The Sixth Annual American Red Cross-Washington College of Law Conference on International Humanitarian Law: A Workshop on Customary International Law and the 1977 Protocols Additional to the 1949 Geneva Conventions, American Journal of International Law and Policy, Vol. 2, 1987, p. 428.
In 1989, a study prepared by the Deputy Director of the US Office of Special Investigations summarized the Office’s assistance in investigations involving three Second World War Nazi war criminals outside the United States. The study reported that:
At the time of [Klaus Barbie’s] extradition [from Bolivia to France], OSI [Office of Special Investigations] was asked by Attorney General William French Smith to investigate and report on allegations concerning Barbie’s post-war relationship with American military intelligence and the latter’s efforts to prevent his arrest by French authorities …
In 1985, OSI strongly supported an effort with West German and Israeli authorities to locate [Josef] Mengele’s whereabouts …
Prompted by a request from the Anti-Defamation League of B’nai B’rith, OSI undertook a formal inquiry into the relationship between the United States government and convicted criminal Robert Jan Verbelen. 
United States, Office of Special Investigations, Deputy Director, Study on “The Purpose and History of the Office of Special Investigations”, 1989, Department of State File Nos. P90 0015-0882, 0932/0935, reprinted in Marian Nash (Leich), Cumulative Digest of the United States Practice in International Law, 1981–1988, US Department of State Publication 10120, Washington, D.C., 1993–1995, pp. 1408–1409.
In 1992, a report on Iraqi war crimes (Desert Shield/Desert Storm) prepared under the auspices of the US Secretary of the Army noted: “The obligation to investigate violations of the law of war committed against allied personnel is subject to the consent of the ally in question, particularly if the alleged violations occurred within the territory of the ally.” 
United States, Secretary of the Army, Report on Iraqi war crimes (Desert Shield/Desert Storm), unclassified version, 8 January 1992, p. 4.
As regards alleged Iraqi war crimes, the report stated that to carry out US directives dealing with the investigation and prosecution of war crimes:
An interagency meeting was held on 30 August 1990 … [The participants] understood that any formal war crimes investigation would depend upon authorization by appropriate authority and, depending on the scope of the investigation, might also require the consent of the host nation …
Detachments selected for mobilization were the 199th Judge Advocate Detachment … and the 208th Judge Advocate Detachment … Elements of the 199th arrived in Kuwait City on 1 March 1991, and upon arrival, reestablished contact with the Kuwaiti Ministry of Justice. Then, with the consent of the Ministry, they contacted members of Kuwaiti resistance groups … The Ministry of Justice was also investigating Iraqi actions during the occupation, To avoid duplicate effort, and in the spirit of cooperation, the mission of the 199th evolved into establishing the nature and extent of Iraqi offences rather than building cases for prosecution. One of the goals was to accumulate and organize the evidence in a fashion that would facilitate preparation of criminal cases should prosecution of war criminals at a later date become an option. 
United States, Secretary of the Army, Report on Iraqi war crimes (Desert Shield/Desert Storm), unclassified version, 8 January 1992, pp. 4–8.
According to the Report on US Practice, it is the opinio juris of the United States that “there is a general obligation to try [persons suspected of war crimes other than members of its own armed forces] or to cooperate with another state willing to try them in accordance with international fair trial standards”. 
Report on US Practice, 1997, Chapter 6.4.
The report also states: “The United States appears to recognize a general obligation on all states to assist each other in the investigation and prosecution of war crimes.” 
Report on US Practice, 1997, Chapter 6.10.