U.S. President Joe Biden called Putin a war criminal on March 16 as news emerged that a theater sheltering hundreds of civilians in the Ukrainian city Mariupol had been levelled.

The International Criminal Court has opened an investigation into war crimes in Ukraine. However, it’s far from certain that anyone will be brought to justice under international law, especially if Russia doesn’t lose the war.

1. What are war crimes?

The definition used by the International Criminal Court in the Hague is extensive. It includes willful killing, torture, rape, forced prostitution, corporal punishment, hostage taking, unlawful deportation, using starvation as a weapon and shooting combatants who’ve surrendered, among many other acts. War crimes can also include using banned weapons such as chemical and biological arms, deliberately attacking civilians and non-military targets, targeting hospitals and other places where the sick and wounded are gathered, looting and carrying out attacks that will cause severe damage to the environment. Russia’s invasion could also be considered a so-called crime of aggression.

2. What’s a crime of aggression?

It’s the planning, preparation and execution by a state military or political leader “of an act of aggression which, by its character, gravity and scale, constitutes a manifest violation of the Charter of the United Nations,” according to the ICC, which adopted it as the fourth crime under its jurisdiction as of 2018, after war crimes, genocide, and crimes against humanity. An act of aggression means “the use of armed force by a state against the sovereignty, territorial integrity or political independence of another State” and can include invasion, occupation and annexation by the use of force, as well as the blockade of ports. The crime applies only to the highest ranking leaders who “exercise control over” or “direct the political or military action of a state.” 

3. How are war crimes prosecuted?

The ICC was born out of an international treaty called the Rome Statute in 2002 as the first permanent, independent arena for holding people accountable for acts of mass inhumanity. It started with 60 countries and its membership has more that doubled since then. Notable countries that have not ratified the treaty are the U.S., China, Russia and India. (The U.S. says putting its citizens under the court’s jurisdiction would violate their constitutional rights.) The ICC can pursue war crimes cases when alleged offenses were committed by a citizen of a member state, or in the territory of a member state or a non-member state that’s accepted the court’s jurisdiction, or when allegations are referred to the court’s prosecutor by the United Nations Security Council. The ICC prosecutor’s office can pursue crimes of aggression upon referral by the Security Council, upon request by a member state, or on its own initiative. 

4. What’s this mean for Ukraine?

Ukraine is not an ICC member but it accepted the court’s jurisdiction for incidents on its territory starting in November 2013. That enabled the court to consider alleged crimes committed during and after Russia’s invasion and annexation of Ukraine’s Crimea peninsula in early 2014. On Feb. 28, the court’s chief prosecutor, Karim Khan, said that based on a preliminary assessment by his office conducted mostly in 2020, “there is a reasonable basis to believe that both alleged war crimes and crimes against humanity have been committed in Ukraine.” He said the investigation he was opening would also encompass any new offenses committed in the expansion of the conflict since Russia’s full-scale invasion. Dozens of countries have asked the ICC to investigate in the wake of that action. 

5. What are the challenges to prosecuting war crimes? 

It’s easy enough to prove that Russian forces have struck civilian targets, including apartment blocks, hospitals, public squares, municipal buildings and a nuclear power plant. A flood of video recordings have been posted on social media, sometimes within minutes of such attacks occurring. And there’s the testimony of Ukrainians experiencing the carnage. But such evidence doesn’t tie specific strikes to specific individuals, which would be necessary for a prosecution. On the other hand, the U.S. has said it is already on the ground searching for evidence of who’s culpable.

6. What are the prospects of trying Russian officials?

Not good. The ICC doesn’t permit trials in absentia, and the court, which has no police force, is unlikely to gets its hands on Putin or his lieutenants. It relies on its member states to make arrests. But they haven’t always respected their obligations to honor the court’s warrants. And the accused could always avoid traveling to any country that might turn them over. The ICC has mainly been able to prosecute war crimes in cases where the accused was on the losing side of a conflict and was turned in by the winning side.