Last week, President Joe Biden called Vladimir Putin a “war criminal” for Russia’s violent invasion of Ukraine. One day later, Secretary of State Antony Blinken agreed with the president’s assessment.

While proving that a state leader committed a war crime is a complicated process, the label is a charged one that carries significant weight coming from a U.S. leader. The Takeaway speaks with Leila Sadat, professor of International Criminal Law at the Washington University in St. Louis and director of the Crimes Against Humanity Initiative, about the process of proving a war crime has been committed and whether more accountability is needed for all nations, including the U.S., who violate the laws of war.