Russia must be held accountable for the destruction it has wrought in its ongoing yearlong war in Ukraine, says Stephen Rapp, a former U.S. ambassador at large for war crimes.

"The use of force or the threat of the use of force is illegal, except in self-defense," Rapp told CBS News in an interview Friday. "And here that clearly occurred."

"This is a scale that we have not seen in conflict since World War II." Rapp said. He noted Ukraine has suffered an estimated $127 billion in damage — homes, schools, public buildings, companies, infrastructure — not to mention "just the horror that's been visited directly on civilians or civilians targeted for torture and rape and detention." He suggested that if there isn't "some kind of accountability," the international community would be giving Russia a kind of "off-ramp" to carry out more aggression.

This week, Rapp was part of a panel of three international legal experts, a kind of "people's court," at The Hague who reviewed evidence and heard testimony from survivors and members of the military against Russian President Vladimir Putin for the crime of aggression in Ukraine.   

Citing evidence from the extensive destruction of civilian and government targets, Rapp said the panel – which does not have any legal authority — confirmed an indictment against Putin for aggression. 

"In this situation, the character is brutal, totally violative of the laws of war. The scale is massive — over a frontier of 2,000 kilometers, 1,200 miles," Rapp said. "And the gravity includes the loss of thousands of civilian lives, tens of thousands of soldiers, the destruction of tens of billions — more than $100 billion, I think, close to $200 billion in infrastructure."

Rapp, who successfully led the prosecution against former Liberian President Charles Taylor for war crimes in Sierra Leone, conceded that prosecuting Putin would be challenging. He said the most likely venue would be the International Criminal Court, or possibly an international tribunal created specifically to handle the crimes in Ukraine.

"We would need to establish a special court," Rapp told CBS News. "The establishment of international tribunal that would include judges around the world that could prosecute him and others. And it could include the Belarusian leaders because they've allowed their territory to be used in this invasion."

As part of a CBS News investigation last year, Rapp noted that Putin had written his Ukraine playbook years ago, in Syria, when his longtime ally, Syrian President Bashar Al-Assad, cracked down on the pro-democracy movement. More than 250,000 civilians have died in the decade-long conflict that followed the Arab Spring movement in 2011.  

Rapp said that Putin has faced no meaningful accountability for Russia's actions in Syria, and the lesson Putin took away was that no one would stop him.

"You could kill your way out of it," Rapp, the former ambassador, said. "And that's the lesson that Russia has taken to heart, too, as it commits these crimes in Ukraine." 

With the Ukraine war now entering its second year, Rapp predicts Putin may taken even more aggressive action this year.

"I don't expect the Russians to improve their tactics. I expect them to be every bit as brutal, if not more so," Rapp said.

As for China's 12-point proposal for peace in Ukraine, Rapp said that given Beijing's human rights records, "I don't think it can be taken at face value. And knowing the Chinese and when they've been involved in various situations, their idea is to put [aside] accountability or justice."

Grace Kazarian contributed to this report.

In:
• Ukraine
• Russia

Catherine Herridge

Catherine Herridge is a senior investigative correspondent for CBS News covering national security and intelligence based in Washington, D.C.

Twitter