Explainer: How to prove genocide?

STORY: (Joe Biden) "Yes I called it genocide"

(Boris Johnson) "Doesn't look far short of genocide to me.”

(Jen Psaki) "He called it genocide."

Washington and Kyiv are accusing Russia of genocide in Ukraine, the gravest and ultimate war crime.

(Volodymyr Zelenskiy) “These are war crimes and they will be recognized by the world as genocide.

But how is it proven?

Genocide has a strict legal definition

and has rarely been proven in court since it was cemented in humanitarian law after the Holocaust.

The 1948 Genocide Convention defines genocide as crimes committed

"with intent to destroy, in whole or in part, a national, ethnical, racial or religious group, as such."

Criminal acts comprising genocide include

- killing members of the group

- causing them serious bodily or mental harm

- creating conditions calculated to destroy them

- preventing births

- or forcibly transferring children to other groups.

Three cases so far have met international courts' threshold:

the Cambodian Khmer Rouge's slaughter of minority Cham people and Vietnamese in the 1970s who were among an estimated 1.7 million dead;

the 1994 mass killing of Tutsis in Rwanda that left 800,000 dead

and the 1995 Srebrenica massacre of some 8,000 Muslim men and boys in Bosnia.

So could genocide be proven in Ukraine?

The International Criminal Court opened an investigation in February

into alleged war crimes and crimes against humanity in Ukraine.

It also has jurisdiction over genocide.

Ukrainian prosecutors say they’ve identified thousands of potential war crimes by Russian forces since February 24 and have compiled a list of hundreds of suspects.

Hundreds of bodies, slain civilians, have been discovered in Bucha since Russian forces withdrew

A discovery that provoked a global outcry.

Ukraine says they were killed by Russian forces during their occupation of the area.

Moscow has denied responsibility and says the West has faked evidence to smear its army.

Russia has called the attack against its smaller neighbor "a special operation" to halt genocide against Russian speakers in Ukraine.

(Vladimir Putin) “It was impossible to continue to tolerate that genocide that lasted for eight years."

To establish genocide, prosecutors must first show that the victims were part of a distinct national, ethnic, racial or religious group.

This excludes groups targeted for political beliefs.

Genocide is also harder to prove than other other violations of international humanitarian law because it requires evidence of specific intent.

Such cases generally take years to reach a verdict.