Analysis - The legal noose is tightening around Russia, with international investigations under way into its invasion of Ukraine.
President Volodymyr Zelensky, of Ukraine, addresses a meeting of the United Nations Security Council in New York City on April 5, 2022. Photo: AFP o/ Timothy Clary
The world is watching on with horror as events unfold, with growing calls for Vladimir Putin and Russia to be held to account.
European Union leaders are denouncing Russia's actions as "massacres, atrocities, genocides", while US President Joe Biden is calling for a war crimes trial.
Here, Prime Minister Jacinda Ardern is choosing her language carefully, referring to evidence pointing to "the fact that there are war crimes being committed by Russia in Ukraine at the hands of the President Vladimir Putin".
Stopping short however, of calling Vladimir Putin a war criminal: "Ultimately it is for the International Criminal Court to make that determination but the evidence is there and New Zealand is supporting the prosecutors and making sure that Russia is held to account", she said.
National leader Chris Luxon is willing to go a step further, saying while "officially you've got to be prosecuted and convicted before you get labelled a criminal, I'd have to say to you the evidence is pretty compelling... I would be quite comfortable calling him a war criminal".
The International Criminal Court (ICC) has been investigating alleged crimes in Ukraine since 2014, and will extend that to the current conflict after referrals from 41 party states, including New Zealand.
University of Otago senior law lecturer Stephen Smith says gathering corroborated evidence will be critically important.
"It's very difficult, if not impossible, for forensic investigators to go in right now and to start gathering evidence.
"But the evidence can come from anywhere, and from any person or any country, so I imagine what the prosecutor is doing now is collecting images, collecting testimony from people being interviewed, about what they saw and what they experience, and they're probably putting out their feelers to other countries to help contribute to this and for countries to submit whatever they can come across."
No easy task with the conflict still raging, and misinformation adding more complexity, Smith says.
"When you can't be on the ground somewhere gathering evidence, if you're just relying on, for all intents and purposes, things you can find on the internet - pictures, those pictures obviously can be faked, videos can be faked, we know.
"And you do need, I think, an accumulation of evidence to sort of overcome this handicap of evidence not being the most solid type of evidence we can have we can gather."
Another difficulty, he says, is a person has to be detained by the court, before it can start trying a case.
"So as long as Vladimir Putin remains free, even if we have boatloads of evidence, there's nothing we can do to start a case against him. That said, the gathering evidence phase can often last several years, one to two years, and then if it comes to trial, a trial can take five, six years is what we've seen so far with the ICC.
Photo: AFP
"So it's a very long-term project, and it's definitely constrained by the fact that we may not be able to detain any suspects, whether it be Putin or other military or political leaders."
And without its own police force, he says, the ICC then relies on other countries to enforce any warrants and arrest people when they arrive in that state.
"So if if Putin remains in power, and he physically remains in Russia, there's not really anything that can be done.
"The only possibility would be a coup that overthrows him, and then his successor could turn him over, or if Putin travels outside of Russia, the country that he's visiting could arrest him," says Smith.
The International Court of Justice issued an order last month expressing its profound concern "about the use of force by the Russian Federation in Ukraine, which raises very serious issues of international law".
In provisional measures it calls on Russia to "immediately suspend the military operations that it commenced on 24 February 2022 in the territory of Ukraine" and to "ensure that any military or irregular armed units which may be directed or supported by it, as well as any organizations and persons which may be subject to its control or direction, take no steps in furtherance of the military operations".
Constitutional law expert and former Prime Minister Sir Geoffrey Palmer says it is an extraordinary judgement.
"I have never seen a more robust decision on provisional measures, and part of the reasons for that, I think, is that it's a pretty open and shut case as to what has happened here."
He cites a cornerstone principle of the United Nations Charter, Article 2 (4) relating to members refraining from "the threat or use of force against the territorial integrity or political independence of any state", with the only way out for the likes of Russia to argue individual or collective self-defence.
The court is limited in what it can do to enforce its orders or directly penalise Russia, but it carries significant moral weight, says Sir Geoffrey.
"What is going to happen next is that the legality of the whole operation in relation to the Genocide Convention will have to be litigated on its merits, and that will be exceedingly embarrassing for Russia.
"One of the most powerful instruments of international law is public shaming, and they're getting a lot of that in relation to what has happened in Ukraine and they will get more if the case comes to be argued on the merits, as I hope it will be."