Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 117. Accounting for Missing Persons
Section A. Search for missing persons
The UK LOAC Manual (2004) states: “Each party must search for persons reported missing by an adverse party and also facilitate such searches by the provision of relevant information.” 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 7.38.