How War Crimes Investigations Work: Evidence, Warrants, and Trial

A war crimes investigation is the formal process by which an authorized body documents serious violations of the laws of armed conflict, identifies those responsible, and builds a case strong enough to prosecute. Understanding how war crimes investigations work means tracking a case through several distinct stages: a legal trigger that opens the file, a preliminary examination, evidence gathering in the field, arrest warrants, trial, and sentencing. The International Criminal Court runs most of these cases today, but UN tribunals and national courts also have authority, and each path has its own rules.

What Counts as a War Crime

The Rome Statute defines war crimes as grave breaches of the Geneva Conventions committed during armed conflict. Article 8 lists them in detail, and the core categories include willful killing of civilians or prisoners of war, torture, hostage-taking, intentionally attacking hospitals or schools, using child soldiers, and widespread destruction of property without military justification.¹ The ICC’s Elements of Crimes document breaks each offense into specific legal elements prosecutors must prove, covering both the physical act and the perpetrator’s mental state.²

The dividing line between lawful combat and a war crime turns on who was targeted and how. A soldier firing on an enemy combatant is engaged in lawful warfare. A soldier who executes a prisoner, bombs a clearly marked hospital, or deliberately starves a civilian population has crossed into criminal territory. The same explosive strike can be lawful when aimed at a military installation and criminal when aimed at a refugee camp. Context is central to every investigation.

Who Has Authority to Investigate

The International Criminal Court

The ICC is the only permanent international court with standing to investigate and prosecute individuals for war crimes, alongside genocide, crimes against humanity, and the crime of aggression.³ It was designed as a backstop, not a replacement for national systems. Its Office of the Prosecutor conducts investigations independently but only steps in when a country with jurisdiction is unwilling or unable to prosecute.

That principle, called complementarity, is set out in Article 17 of the Rome Statute. The ICC declares a case inadmissible when a competent national court is genuinely investigating or prosecuting. It only takes over when the national process is a sham designed to shield the accused, has stalled through unjustified delay, or when the country’s judicial system has substantially collapsed.⁴ Most jurisdictional disputes play out here, with governments arguing their own courts are handling the matter and the ICC judging whether those proceedings are genuine.

UN Security Council Tribunals

The UN Security Council can create temporary tribunals for specific conflicts through resolutions adopted under Chapter VII of the UN Charter. The International Criminal Tribunal for the former Yugoslavia (Resolution 827 in 1993) and the International Criminal Tribunal for Rwanda the following year are the leading examples.⁵ Chapter VII addresses threats to international peace and gave these tribunals power to compel cooperation from member states.⁶ Both tribunals have completed their work, but their procedural framework shaped how the ICC operates today.

National Courts and Universal Jurisdiction

Any country can investigate and prosecute grave breaches of the Geneva Conventions regardless of where the acts occurred, who committed them, or who the victims were. This is universal jurisdiction, rooted in the idea that certain crimes are so serious every nation has an interest in punishing them. The Geneva Conventions and their Additional Protocols require signatory states to adopt laws enabling such prosecutions. Several European countries have used universal jurisdiction in recent years against individuals linked to the Syrian conflict and others, often after suspects entered the country as asylum seekers.

The United States has its own federal war crimes statute, 18 U.S.C. § 2441, giving federal courts jurisdiction when the victim or offender is a U.S. national, lawful permanent resident, or member of the U.S. armed forces, or when the offender is found on U.S. soil regardless of nationality.⁷ The Justice Department’s Human Rights and Special Prosecutions Section handles cases against people who commit atrocities abroad and then enter the United States.⁸ One important boundary: under the American Servicemembers’ Protection Act of 2002, the United States does not recognize ICC jurisdiction over U.S. nationals and actively resists ICC involvement with American personnel.⁹

How an Investigation Gets Opened

Under Article 13 of the Rome Statute, an ICC investigation requires one of three specific triggers. A State Party can refer a situation on its territory to the Prosecutor. The UN Security Council can refer a situation under Chapter VII, and this mechanism reaches beyond the ICC’s usual jurisdictional limits to cover non-member states.¹ Third, the Prosecutor can open an investigation independently under what is called proprio motu authority, with an added safeguard: a Pre-Trial Chamber of three judges must authorize it, finding a reasonable basis to proceed before field work begins.¹⁰

Whichever trigger starts the process, the Prosecutor first conducts a preliminary examination. That assessment asks whether the alleged crimes fall within the court’s jurisdiction, whether they are grave enough to justify international prosecution, and whether they are already being genuinely handled by a national court. Only after clearing those thresholds does a formal investigation begin.

What Evidence Investigators Collect

Three types of evidence do the heavy lifting in a war crimes case, and each addresses a different element prosecutors need to prove.

Forensic Evidence

Specialists analyze mass burial sites, examine remains to determine cause of death, and document physical conditions at crime scenes. The critical forensic question is often whether victims were non-combatants rather than active participants in fighting. That single determination can separate a war crime from a lawful act of war. Physical evidence provides the objective record that supports or undermines the competing narratives offered by the parties involved.

Witness Testimony

Survivor and eyewitness accounts supply the human context forensic data alone cannot capture. Prosecutors need testimony detailed enough to place the accused at the scene, connect them to the chain of command, or establish their knowledge of crimes committed by subordinates. Witness statements are the primary tool for proving intent, showing that prohibited acts were deliberate rather than accidental consequences of combat. Investigators use standardized interview techniques to preserve reliability for cross-examination at trial.

Documentary and Digital Evidence

Military logs, internal communications, and command orders establish the decision-making trail that links leadership to crimes on the ground. This evidence is essential for proving command responsibility, the legal theory that a superior who knew or should have known about crimes and failed to prevent them bears criminal liability. Satellite imagery, intercepted communications, and social media content increasingly supplement traditional documents. Digital evidence requires rigorous authentication, with metadata verified to confirm time, location, and integrity of recordings. International investigations now follow established protocols for identifying, collecting, preserving, and analyzing open-source digital information to meet evidentiary standards at trial.

From Field Work to Arrest Warrants

Once an investigation is formally opened, the ICC deploys specialized teams of forensic experts, legal analysts, and investigators to the regions where alleged crimes occurred. Every piece of evidence recovered follows strict chain-of-custody protocols. Items are documented, cataloged, and transported to secure facilities. A single break in the chain can make evidence inadmissible, so this procedural rigor is not optional.

When the evidence is sufficient to identify specific perpetrators and their roles, the Prosecutor applies to the Pre-Trial Chamber for arrest warrants or summonses to appear. The documents lay out the specific charges under the Rome Statute and the supporting evidence.¹

Enforcing those warrants is where the system’s limits show. The ICC has no police force. It depends entirely on member states to arrest and surrender suspects. The Rome Statute obligates states parties to cooperate fully, including complying with arrest and surrender requests, and when a state fails to cooperate the court can refer the matter to the Assembly of States Parties or back to the Security Council.¹ Those referrals often lack teeth. INTERPOL assists by issuing Red Notices, requests to law enforcement worldwide to locate and provisionally detain a person pending extradition or surrender, but a Red Notice is not an international arrest warrant, and each country decides independently whether to act on it.¹¹

What Slows Cases Down

War crimes investigations face obstacles domestic criminal cases rarely encounter. The most fundamental is state cooperation. The ICC has no executive enforcement power, no investigators with arrest authority, and no ability to compel a government to hand over documents or suspects. Without cooperation, investigations stall. No arrests, no trials.

Geography and security compound the problem. Investigators must collect evidence in conflict zones or post-conflict regions thousands of kilometers from The Hague, where travel is dangerous and security volatile. The people who order atrocities rarely leave a clear paper trail. Leaders directing genocide or systematic violence typically work hard to destroy evidence linking them to criminal orders. Reconstructing that command chain after the fact, often from fragmentary records and frightened witnesses, is difficult work.

Witness protection creates its own dilemma. Survivors willing to testify often face serious threats. The court uses redactions to protect them, but heavy use of redactions can undermine the accused’s right to confront the evidence. Balancing witness safety against fair trial requirements runs through every major case.

Protections Built Into the Process

Article 68 of the Rome Statute requires the court to take appropriate measures to protect the safety, physical and psychological well-being, dignity, and privacy of victims and witnesses, with particular attention to cases involving sexual violence or violence against children.¹ When public testimony would endanger a victim or witness, the court can close proceedings or allow evidence through electronic means. The ICC’s Victims and Witnesses Section runs a protection program and uses trauma-informed approaches with survivors.¹² Victims who cannot afford legal representation receive it free of charge, and they have the right to participate in proceedings that affect their personal interests through legal representatives.

The accused receives parallel protections. During investigation, a suspect has the right to be informed of the suspicion, to remain silent without that silence counting against them, to have counsel present during questioning, and to be free from coercion.¹ At trial, Article 67 guarantees a public and impartial hearing, adequate time and private access to counsel, trial without undue delay, the ability to examine witnesses and present a defense, a competent interpreter at no cost, and the right against self-incrimination. Under Article 66, the Prosecutor bears the entire burden of proving guilt beyond a reasonable doubt. The presumption of innocence is absolute, and denying a protected person a fair trial is itself classified as a grave breach under the Geneva Conventions.¹³

Sentencing, Appeals, and Reparations

A person convicted of war crimes by the ICC faces imprisonment of up to 30 years, or life imprisonment when the extreme gravity of the crime warrants it. When someone is convicted of multiple offenses, the court pronounces a sentence for each crime and a combined sentence that cannot exceed 30 years or life.¹⁴ The death penalty is not available. Sentences are served in countries that have agreed to accept ICC prisoners.

Both the convicted person and the Prosecutor can appeal. Grounds include procedural errors, errors of fact or law, and, for the defense, any other ground affecting the fairness or reliability of the proceedings. Either side can also appeal the sentence itself if it is disproportionate. Decisions on jurisdiction and admissibility, as well as pre-trial rulings that significantly affect fair proceedings, are also appealable.¹

After conviction, the court can order reparations directly to victims, including restitution, compensation, and rehabilitation. The court determines the scope of harm and sets out the principles guiding its order, taking into account representations from the convicted person, victims, and other interested parties.¹⁵ Reparations are often channeled through the Trust Fund for Victims, established under Article 79 of the Rome Statute.¹⁶

1
International Criminal Court. Rome Statute of the International Criminal Court
2
International Criminal Court. Elements of Crimes
3
International Criminal Court. How the Court Works
4
International Committee of the Red Cross. Rome Statute Article 17 – Issues of Admissibility
5
International Criminal Tribunal for the former Yugoslavia. Security Council Resolution 827
6
United Nations. United Nations Charter – Chapter 7
7
Office of the Law Revision Counsel. United States Code Title 18 Section 2441 – War Crimes
8
United States Department of Justice. Human Rights and Special Prosecutions Section
9
Office of the Law Revision Counsel. United States Code Title 22 Chapter 81 – American Servicemembers Protection
10
International Criminal Court. Judicial Divisions
11
INTERPOL. View Red Notices
12
United Nations Office on Drugs and Crime. International Criminal Court Submissions – UNGA Resolution 78/227
13
International Committee of the Red Cross. Customary IHL Rule 100 – Fair Trial Guarantees
14
United Nations. Rome Statute – Part 7 Penalties
15
International Committee of the Red Cross. Rome Statute Article 75 – Reparations to Victims
16
International Criminal Court. Trust Fund for Victims