A few weeks ago I sat down in the US State Department with President Joe Biden's ambassador for Global Criminal Justice.

Beth Van Schaack is the woman the president has tasked with pursuing the Russian leader to the dock.

I asked her: "Many will see it as inconceivable that Vladimir Putin could be put on trial for war crimes. How important is it to pursue justice however unlikely it may be?"

Ukraine war latest: Judges issue arrest warrant for Putin over alleged war crimes

"Well…" she said, disagreeing with the premise of my question… "Augusto Pinochet, Slobodan Milosevic, Hissene Habre of Chad? I don't think any of those men thought they would ever see the inside of a courtroom and every single one of them did…

"We need to play a long game here. One never knows how situations will change.

"And as long as you have collected evidence, produced dossiers on responsible individuals, you can stand ready until a court somewhere around the world is able to suddenly assert jurisdiction, and then the prosecutors will move."

A global effort for justice

Ms Van Schaack leads the US Office of Global Criminal Justice. Her job is to advise the Secretary of State (Antony Blinken) and other leadership around the US on issues of justice and accountability.

Her team has worked with prosecutors and human rights organisations globally to investigate and collate evidence from Ukraine, building a case against Russian individuals leading all the way to Mr Putin himself.

"We've now seen war crimes being committed on a systemic basis across all areas where Russia's troops are deployed; terrible stories, credible, corroborated by a UN Commission of Inquiry and others, of civilians being deliberately targeted of disproportionate force being used, civilians being killed in Russian custody, POWs being killed, and then efforts to cover up these crimes…" she told me.

"We've seen the satellite imagery and other imagery even just taken from ordinary CCTV cameras on people's front yards of bodies lying, hands tied behind their back clear evidence of either torture, or summary execution-style killings.

"There's also the attacks on a theatre, on a train station of people fleeing the conflict. You have attacks on ordinary convoys of civilians trying to get out; people just going to work, carrying grocery bags with their groceries strewn around the dead body…."

She continued: "These images do stick in one's head. They're searing, searing images, and all of them now are being collected by the prosecutor general but other investigative organisations including the UN Commission of Inquiry, the International Criminal Court, and the European prosecutorial authorities who are increasingly united around the imperative of justice."

Connecting the dots

Ambassador Van Schaack explained that crimes can be linked and lines are drawn to show that there are reasonable grounds to believe that Mr Putin was, through his authority, responsible for these crimes.

"We need to connect the crimes we're seeing on the ground - that we have very clear digital evidence of - with those and in the position of command and control.

"So go up the chain of command - who ordered these offences? Who allowed them to be committed? Who has failed to prosecute and investigate those deemed most responsible? Who has failed to properly supervise their subordinates? That's now the challenge - that linkage evidence."

On the likelihood of an arrest of officials around President Putin, she said: "I think what drives everyone in this field is the idea that someday, circumstances will change.

"Someone will slip up, someone will travel, they will slip in with a false identity, and individuals will recognise them on the street, they will contact law enforcement and law enforcement will be ready, because we will have collected evidence from the start of this terrible conflict, precisely to be ready for that moment."

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Different avenues to justice

Ms Van Schaack described several avenues that will be pursued to seek justice and there are three currently operational as we speak.

"Number one is the Prosecutor General in Ukraine, investigating these cases in his own domestic system with his colleagues, with support from the international community. The UK, the EU and the United States have brought a number of cases, have achieved some convictions, and a number of cases are ongoing," she said.

"Avenue number two is the International Criminal Court currently seized of this matter, looking at cases that may be more appropriate for an international court to take."

This is the avenue through which the arrest warrant for Mr Putin has now been issued.

She continued: "Avenue three, which should not be forgotten, is domestic courts around the world. Many European states have formed a joint investigative team to share information directly with each other about the condition of potential abuses, and potential responsible individuals."

Ukraine has also sought some sort of mechanism to be able to prosecute the specific crime of aggression.

On this, Ms Van Schaack said: "This is a high priority for Ukraine, because they see that initial act of aggression as being the original sin that unleashed all of the other war crimes and atrocities that we're seeing around the country."