Once an allegation is received, the UN will carry out an administrative investigation. The Office of Internal Oversight Services (OIOS), the independent investigative arm of the UN, is the sole body in the UN responsible for such investigations, but may refer the allegation to other investigative authorities, depending on the category of personnel and the gravity of the allegations.

For investigation purposes, OIOS has grouped allegations into Category 1 and Category 2, depending on the risk such cases present to the organisation. Category 1 includes: all offences related to sexual exploitation and abuse including rape, transactional sex, exploitative relationships and sexual abuse, cases involving risk of loss of life to staff or to others, conflict of interest, gross mismanagement, bribery/corruption, illegal mineral trade, trafficking with prohibited goods, life threat/murder, abuse or torture of detainees, arms trade, physical assault, forgery, embezzlement, major theft/fraud, use, possession or distribution of illegal narcotics, waste of substantial resources, entitlement fraud and procurement violations.

Category 2 includes: discrimination, harassment, sexual harassment, abuse of authority, abusive behaviour, basic misuse of equipment or staff, simple theft/ fraud, infractions of regulations, rules or administrative issuances, traffic-related violations, conduct that could bring the UN into disrepute and breaking curfew.

OIOS is responsible for investigating all Category 1 allegations, including sexual exploitation and abuse, except for military contingents, for whom special provisions apply. Category 2 allegations may be investigated by the Special Investigation Unit (SIU), Military Police, UN Police and ad-hoc panels.

The UN Office of Human Resources Management in the Department of Management takes decisions concerning disciplinary measures for civilian personnel.

When allegations of misconduct involving military and police personnel are substantiated, the UN may repatriate the individuals concerned and ban them from future peacekeeping operations. The disciplinary sanctions and any other judicial actions remain the responsibility of the national jurisdiction of the individual involved.

Members of military contingents deployed on peacekeeping missions remain under the exclusive jurisdiction of their national government. The responsibility for investigating an allegation of serious misconduct and taking subsequent disciplinary action rests with the Troop Contributing Country, in accordance with the revised model memorandum of understanding, endorsed by the General Assembly in 2007. The Troop Contributing Country involved must then report back to the UN on the outcome of misconduct investigations and actions taken.