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Even before the outrage over hundreds of civilians reportedly killed in Bucha, Ukraine was accusing Russia of committing a number of war crimes, and many experts have backed those claims.
President Biden on Monday called for Russian President Vladimir Putin to face a war crimes trial.
"You saw what happened in Bucha," Biden said. "He is a war criminal. But we have to gather the information. We have to continue to provide Ukraine with the weapons they need to continue the fight. And we have to gather all the details, so this can be an actual ... have a war crime trial," he said.
But experts warn it would be a difficult and long process to bring Putin to account — and even harder to enforce any actions against him.
Here's a rundown of the legal situation as the international community looks for ways to hold Russia accountable for the killings, widespread destruction and human rights abuses that have been documented in Ukraine.
Could Putin be held responsible individually? What about Russia?
"It's unlikely" that Putin would face a war crimes trial at the highest international levels, said Kelebogile Zvobgo, the founder and director of the International Justice Lab who is an assistant professor of government at William & Mary.
An array of international judicial institutions have jurisdiction over abuses that Putin's military is accused of carrying out in Ukraine. But those courts differ in how they work and how their rulings are enforced — and few have any leverage over Russia.
The International Court of Justice at The Hague
The U.N.'s highest court was created to resolve inter-state disputes, not to rule on cases involving individuals. Any decisions it makes are implemented by the U.N. Security Council — but Russia holds a critical veto vote on that panel.
Ukraine formally asked the court to order Russia to halt its war on Ukraine early in the conflict, citing the 1948 international convention banning genocide. But Russia's representatives didn't show up to the hearing. The court granted Ukraine's request, but it has no way to enforce its order for Russia to halt its invasion.
The International Criminal Court
Days after Russian forces invaded Ukraine, the ICC's top prosecutor said there was "reasonable basis to believe" war crimes and crimes against humanity were being committed in Ukraine, and a formal investigation would begin.
In theory, the ICC would be the court that could handle any potential prosecution of Putin, Zvobgo said. But she added, "they don't have the best track record because nobody wants to turn over heads of state."
"This is a criminal court. This one is actually concerned with individuals. But the challenge is, you have to actually get the people to the place," Zvobgo said. "Who would be willing to arrest and transfer Putin to The Hague — if he even left Russia?" she added.
The European Court of Human Rights
The international court was created by the Council of Europe to handle cases against individuals and groups, as well as countries. But Russia has shown only spotty compliance with its past rulings. And the chances of future compliance grew even more remote in mid-March, when Russia was expelled from the Council of Europe altogether.
To Zvobgo, Russia's exit from the council — and the court's jurisdiction — represents a missed opportunity.
"You could say, well, they weren't going to comply with any decision, so it doesn't matter," Zvobgo said. "But I think even just having accountability, having verdicts for Ukraine, for Ukrainian victims, would have been really helpful from just an acknowledgement perspective — which can be exceedingly powerful." That's true, she added, even when a nation refuses to follow the court's remedies.
Zvobgo said she thinks the International Criminal Court will consider charges against Russia — but she warned that the process would likely take years and years before a final decision emerges.
As an example, she noted that in March, the ICC issued arrest warrants in a case centering on alleged war crimes in and around the territory of South Ossetia, Georgia — a case that began with an examination in 2008, when the actions occurred.
Are any other avenues open to pursue charges against Putin's regime?
"My best bet, and I think the great promise of international justice for abuses in Ukraine, is going to be European courts" using the universal jurisdiction doctrine to prosecute Russians, Zvobgo said.
Universal jurisdiction is the legal concept that a country's domestic court system can take up cases against people who are accused of committing grievous offenses, such as war crimes and genocide, even if the alleged crime happened outside of the prosecuting country's territory. The rationale behind the idea is that the authority and duty to prosecute serious crimes extends beyond international borders because people who commit such acts are deemed hostes humani generis — "enemies of all mankind."
The doctrine was used when Spanish courts tried dictator Augusto Pinochet, over abuses when he ruled Chile; more recently, it allowed a German court to sentence a Syrian intelligence officer to life in prison for murders and torture that took place in Damascus.
"We see countries like Poland that are already initiating investigations and have already communicated that they are interested in addressing war crimes and other atrocities," Zvobgo said.
Another approach to hauling Russians into court would be for the U.S. and its allies, such as France, U.K. and Germany, to try to create an ad hoc international tribunal outside of the U.N., similar to the Nuremberg and Tokyo war crimes trials. But such an undertaking would pose a number of challenges — including questions of legitimacy, in Zvobgo's view.
What is a war crime exactly?
The distinctions between war crimes, genocide and crimes against humanity depend on how widespread and systematic the actions are, and the intent behind them.
Pierre-Richard Prosper, a war crimes prosecutor and a former U.S. ambassador-at-large for war crimes, said the international community should be more concerned about responding to the situation in Ukraine, rather than labeling what's happening there.
"What we need to be doing is really focusing on the actions themselves," he told NPR's Morning Edition. "It is clear that atrocities are being committed, it is clear that ... there are violations of the laws of war."
"That should be sufficient for nations — not just the West, not just the United States, but the entire international community — to act," he said.
It can be complicated to distinguish between different heinous crimes, which are forbidden in a number of legal documents such as the Geneva Conventions and the Rome Statute of the International Criminal Court.
A war crime can involve the willful killing of an individual, or abuses such as torture, property destruction, sexual violence, or forced displacement during a conflict. It can be perpetrated by individual soldiers — but it doesn't necessarily reflect their military or country.
In contrast, crimes against humanity often signify widespread attacks with intentional direction. And killings and other actions can be seen as genocide when a group is targeted because of their racial, ethnic, national or other identifying characteristics — with the intention of destroying part or all of that group.
How should the world react to signs of atrocities?
The word genocide can trigger a powerful reaction in people, perhaps due to atrocities such as the Holocaust, or other genocides in Rwanda and elsewhere.
When an offense is labeled as genocide, it's also meant to trigger international responses, such as the "responsibility to protect." The concept deems that outside of any alliances, the global community has the responsibility "to end the worst forms of violence and persecution" and protect at-risk populations, according to the U.N.
International courts can move slowly to reach a determination, Prosper said — but he added that individual nations should move much more quickly.
"When you see civilians being killed, their hands tied behind their backs and executed, that should be sufficient," he said, in an apparent reference to the scenes in Bucha. "We have seen the international community take actions in other areas when civilians have been in harm's way. So this should not be any different."
Those actions should focus on supporting Ukraine's government and helping it defend itself, he said.
"We need to continue to shine a light on the actions of the Russians, the Russian government, because we have to make sure that this is undeniable," Prosper said.
"Hopefully, it will begin to not only curb the action, but promote an action of accountability. Hopefully, it will promote dissent from within, where the Russian people themselves see that that there is a problem."
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