What counts as a war crime and why they're so hard to prosecute

What counts as a war crime

• War crimes include serious violations of international law or customs committed against civilians and/or certain combatants in armed conflict, according to the UN.
• No single international law, document or treaty codifies all war crimes. The rules of war have been changed and expanded since the Geneva Conventions were significantly updated following World War II.
• Examples of war crimes include intentionally targeting civilian populations, torture, taking hostages, rape and other sexual violence, enlisting or conscripting children, and intentionally directing attacks against buildings dedicated to religion, education, art and other cultural aspects of society.

Who investigates and prosecutes war crimes?

• Any country can investigate and prosecute war crimes within its national framework. A German court, for example, convicted a former Syrian officer in January for aiding and abetting crimes against humanity during the Syrian war.
• The International Criminal Court, established by the Rome Statute, has jurisdiction over individuals charged with war crimes, genocide and crimes against humanity. Notably, Russia, Ukraine and the U.S. are not state parties to the ICC.
• The UN can set up a special inquiry commission to investigate war crimes and then hand over the cases to some kind of international war crimes tribunal. A group of concerned nations can also set up special tribunals following the example set in Nuremberg after World War II.

The sentencing of convicted war criminals typically ranges from long-term imprisonment to death, depending on the guidelines set out by the court or country in which the trial is held.

• A UN-backed international court, for example, convicted former Liberian President Charles Taylor in 2012 of aiding and abetting war crimes and crimes against humanity in Sierra Leone. He is serving a 50-year sentence in a U.K. prison.

Why war crimes are hard to prosecute

• Investigating and prosecuting war crimes can take years, often leading to frustration for victims.
• War crimes contain two primary elements: a violation that took place during an armed conflict, and "intent and knowledge" of the act and conflict, according to the UN.

While establishing that a violation took place isn't always hard, it can sometimes be difficult to prove certain crimes like the targeting of civilians, according to Alex Whiting, a Harvard Law School visiting professor and deputy specialist prosecutor at the Kosovo Specialist Prosecutor’s Office in The Hague.

• "You have to first establish that there was no military target nearby, and if there was, the force was disproportionately used, and then you have to prove that it was intentional," says Whiting, who previously served as an ICC prosecutor.
• Whiting notes that because more of these incidents are shared live or captured via phones, bringing cases forward becomes easier and faster.
• Still, the main challenge in prosecuting war crimes is usually determining who is responsible, Whiting says. This becomes especially hard when trying to hold high-profile leaders accountable, as they're often not at the scene of an alleged violation.

The allegations against Russia in Ukraine

• Russia has been accused of intentionally targeting civilians and health facilities, taking hostages, and other international law violations.
• Secretary of State Antony Blinken said on March 23 that "based on information currently available, the U.S. government assesses that members of Russia’s forces have committed war crimes in Ukraine."

• Ukrainian President Volodymyr Zelensky has accused Russia of committing war crimes in its siege of the port city Mariupol. A theater and an art school sheltering civilians there have been bombed, and a maternity ward was attacked.
• The Kremlin has repeatedly denied it is targeting civilians.
• Zelensky also accused Russia of committing war crimes in other cities, including Kharkiv, where Human Rights Watch in early March said Russia fired cluster munitions into at least three residential areas.

• Russia, which is not a party to a treaty banning cluster munitions, in early March denied the use of these weapons, per AP.
• What to watch: Based on the evidence coming out of Ukraine, Whiting says he "would not be surprised if there were some cases against some specific commanders in the Russian military that were brought in the next few months."

What happened in Bucha?

• As Ukrainian forces retook areas in the Kyiv region in early April, officials and independent photographers documented bodies of civilians — some with their hands tied behind their backs — strewn in the streets of the city of Bucha. A mass grave was also found.
• Zelensky has labeled what happened in Bucha as "genocide."
• Russia's defense ministry has said without evidence that Ukraine staged a "fake attack" in Bucha.
• In the case of Bucha the challenge is "not so much to prove that [war] crimes occurred," but rather proving "who was responsible [and] how high does this [responsibility] go up," says Whiting.

What about Putin?

• Biden on March 16 explicitly called Putin a "war criminal." He repeated that label on April 4, saying Putin should face a war crimes trial over the reported atrocities in Bucha.
• Russia in March called Biden's statements "unacceptable," warning ties between the two countries are on "the verge of breaking."

• Even if prosecutors can show that high-level officials and/or Putin directed or were aware of orders to target civilians or other actions that may constitute war crimes, a trial cannot be conducted unless the official is in custody.
• "This is going to be really complicated unless a war criminal is captured on the ground in Ukraine," says Mark Drumbl, director of the Transnational Law Institute at the Washington and Lee School of Law.

Where it stands

• The ICC in late February announced it was opening an investigation into possible war crimes committed in Ukraine after referral by dozens of member countries.
• Ukraine, while not a state party to the ICC, in 2015 accepted jurisdiction of the court for possible war crimes and crimes against humanity committed since Russia's annexation of Crimea in 2014.
• Separately, the UN Human Rights Council voted in March to set up an independent international commission of inquiry to investigate alleged human rights violations in Ukraine. Russia called the move a "waste of resources."

The bottom line

• International law "gives us a moral vocabulary to talk about what's happening in Ukraine," says Drumbl. This "triggers a much faster" response from the international community, including sanctions and boycotts, Drumbl says, "even in the impossibility of criminal trials."
• Whiting adds that an investigation "sends a message to the victims that they're being seen and recognized" and shows "perpetrators that they're being watched."

Go deeper:

• Axios explains Ukraine
• The latest on the Russia-Ukraine crisis

Editor's note: This story has been updated with additional details from the U.S. State Department, as well as details from Bucha.