“They have never been punished and they have never been brought to the war tribunal,” Mr Fedoruk told Washington think tank the Wilson Centre.
Russian forces “were saying the Russian phrase 'the war will write it off, so kill, rape and loot' … we have to do everything possible to punish such crimes".
According to Ukraine and charities, Russian forces left a trail of evidence during their occupation of Bucha, a town about 30km north-west of Ukraine’s capital Kyiv, from March 4 to 31, 2022.
The Kremlin has strenuously denied any accusations related to the murder of civilians, including in Bucha, where it said the graves and corpses had been staged by Ukraine to tarnish Russia.
A report from Human Rights Watch found extensive evidence of “summary executions, other unlawful killings, enforced disappearances and torture, all of which would constitute war crimes and potential crimes against humanity” by Russian forces against Ukrainian civilians there.
“Nearly every corner in Bucha is now a crime scene, and it felt like death was everywhere,” Richard Weir, crisis and conflict researcher at Human Rights Watch, said on the release of the report in April.
While introducing Mr Fedoruk, former US ambassador and Wilson Centre president Mark Green said 458 bodies were recovered from the town's ruins, with 419 bearing signs of torture and other mass trauma.
“Bucha represents the world's first definitive look at how the Russian military employs atrocity in Ukraine as a deliberate tactic,” Mr Green said.
Mr Fedoruk went into hiding to co-ordinate assistance for those few thousand people who stayed behind during the Russian occupation.
His interviews with international media over the spring and summer of 2022 helped to spread the word of Russian war crimes.
He recalled what he described as “my beautiful and blossoming city of Bucha” in his remarks on Monday.
“Before the invasion, our city was developing with accordance to the economical possibilities of our country. We're building schools, kindergartens, we're raising children,” said Mr Fedoruk.
“But on February 24, we couldn't have thought that we would wake up with missiles attacks.”
The Wilson Centre discussion also centred on Bucha's efforts to rebuild in the aftermath of devastation.
“The task now before the mayor and his team … is now one of reconstruction and bringing Bucha's residents back home. Their work is not only about restoring buildings and infrastructure, but also documenting Russian war crimes and atrocities and helping the town to come back together as a community,” Mr Green said.
“We will rebuild, but we will not forgive [Russia] for what happened,” Mr Fedoruk said.
“Those who have given orders, and all those who have actually done those crimes, must be punished.”