ICAO Annex 13
CHAPTER 5. INVESTIGATION
RESPONSIBILITY FOR INSTITUTING AND CONDUCTING THE INVESTIGATION
ACCIDENTS OR INCIDENTS IN THE TERRITORY OF A CONTRACTING STATE

State of Occurrence
5.1 The State of Occurrence shall institute an investigation into the circumstances of the accident and be responsible for the conduct of the investigation, but it may delegate the whole or any part of the conducting of such investigation to another State or a regional accident investigation organization by mutual arrangement and consent. In any event, the State of Occurrence shall use every means to facilitate the investigation.

RESPONSIBILITY OF THE STATE CONDUCTING THE INVESTIGATION
General
5.4 The accident investigation authority shall have independence in the conduct of the investigation and have unrestricted authority over its conduct, consistent with the provisions of this Annex. The investigation shall normally include:

a) the gathering, recording and analysis of all relevant information on that accident or incident;
b) if appropriate, the issuance of safety recommendations;
c) if possible, the determination of the causes and/or contributing factors; and
d) the completion of the final report.