Related Rule
Practice Relating to Rule 161. International Cooperation in Criminal Proceedings
Section A. Cooperation between States
Sweden’s IHL Manual (1991) notes that the 1977 Additional Protocol I “states that the contracting parties shall to the greatest extent possible assist each other in connection with penal procedures instituted as a consequence of grave breaches of the [1949] Geneva Conventions or [the 1977 Additional Protocol I]”. 
Sweden, International Humanitarian Law in Armed Conflict, with reference to the Swedish Total Defence System, Swedish Ministry of Defence, January 1991, Section 4.2, p. 97.