(NewsNation) — President Joe Biden explicitly called Russian President Vladimir Putin a “war criminal” for the unfolding war in Ukraine, where hospitals and maternity wards have been bombed. But declaring someone a war criminal is not as simple as it seems. There are set definitions and processes for determining who’s a war criminal and how they should be punished.

The White House had been avoiding applying the designation of war criminal to Putin, saying it requires investigation and an international determination. After Biden used the term, White House press secretary Jen Psaki said the president was “speaking from his heart” and renewed her statements that there is a process for making a formal determination.

Essentially, the International Criminal Court is the only one in the world that can prosecute individuals for committing atrocities or crimes of aggression when that person’s own country won’t or is incapable of doing so.

The key is that the ICC charges individuals for responsibility in crimes committed by their armies. It’s not the nation overall. Essentially, the ICC would have to prove that Putin ordered his military to commit these crimes, knew about them or should have known. If prosecutors can prove that, he can be found guilty.

War crimes, as defined in the aftermath of World War II, include: willfully killing, torture, extensive destruction not justified by military means, compelling a prisoner of war to serve in its enemy’s army and hostage-taking.

Russia is specifically accused of targeting civilian populations, which is not justified by military means, like the maternity hospital in Mariupol and Freedom Square in Kharkiv.

Proving intent to commit a war crime can be extremely difficult. Since the court’s founding, 45 individuals have been prosecuted for committing war crimes or crimes against humanity.

The last time a sitting president was indicted on war crimes was in 2020 when Kosovo’s president was charged with committing war crimes during the Yugoslavia war.

It’s not clear if Putin would be put on trial if convicted. Russia does not recognize the jurisdiction of the International Criminal Court and would not send any suspects to the court’s headquarters in The Hague, Netherlands. The U.S. does not recognize the authority of the court, either. Putin could be tried in a country chosen by the United Nations or by the consortium of concerned nations. But getting him there would be difficult.