THE HAGUE: Ukrainian President Volodymyr Zelenskyy, during a surprise visit to The Hague Thursday, insisted that a special international tribunal should be created to prosecute Russian President Vladimir Putin for "crimes of aggression".
But what could such a prosecution look like? Here are five issues that would need to be resolved.
The International Criminal Court in March issued an arrest warrant for Putin, accusing him of unlawfully deporting Ukrainian children, which is a war crime.
But the Hague-based ICC cannot pursue aggression crimes charges against Moscow as it is not a signatory of the court's founding treaty, the Rome Statute.
Summed up, the Rome Statute defines this crime as the attack of one state on another, planned by a political or military leader in breach of the UN Charter, which among other things forbid the use of force internationally.
Legal experts say that with the full-scale invasion of Ukraine in February last year, President Putin "shredded" this Charter commitment.
"Impunity is the key to aggression... the beginning of evil," Zelenskyy said in a speech during his visit. A prosecution for the invasion would deter future perpetrators, he argued.
Zelensky said an international tribunal would be "correcting the loopholes that unfortunately exist in law".
Experts however warn that getting such a tribunal off the ground would not be easy.
One possible avenue would be to get overwhelming support at the 143-state UN General Assembly (UNGA) - even if Russia would use its permanent seat on the UN Security Council to veto their involvement.
And support could be limited for any tribunal that involved only European states or a regional organisation such as the EU, say experts.
Stephen Rapp, former US envoy on war crimes, said the "most important thing to achieve this is that countries outside Europe recognize that they have an interest in maintaining the sovereignty and territorial integrity of all countries".
The ICC, which started work in 2002, is already investigating war crimes and crimes against humanity committed in Ukraine.
The ICC's chief prosecutor Karim Khan has opposed a special tribunal for Ukraine.
Creating a special tribunal could be setting him up to fail, he said in December. Instead, he urged the international community to focus on supporting his own investigation.
Khan has suggested that ICC member states should look at ways of closing the loophole so they can prosecute a country even if it is not a member.
But amending the Rome Statute most likely could not be done retroactively.
And even if it was done, the war in Ukraine would "long be finished," Rapp warned.
Many of Ukraine's allies, including the United States, have expressed support for the idea of trying Russian aggression with international funds and staff, but "rooted in the Ukrainian justice system".
Hybrid tribunals incorporates both international law as well as local legislation -- and usually function within the country where the crimes are committed.
There are exceptions to this though, including the Special Tribunal for Lebanon and the Kosovo Specialist Chambers, both based in or near The Hague.
Zelenskyy however strongly opposed the idea.
"Our clear-cut position is... and I expressed my opinion on this: we are going to work without any form of hybrid (court) altogether," he said Thursday.
While Zelenskyy said he was confident the Russian leader would end up on trial and "convicted" in The Hague, experts have warned it may be a tall order.
Putin was unlikely to end up in the dock for crimes "unless there is a regime change in Russia", said Cecily Rose, assistant professor of public international law at Leiden University.
Yet history has seen several senior figures who have ended up in the dock on war crimes charges against all odds.
One example is former Serbian president Slobodan Milosevic, who died in his cell in The Hague in 2006 while on trial for genocide at the Yugoslav war crimes tribunal.
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