More than 200 Ukrainian prisoners of war have died in Russian captivity since the start of the full-scale invasion, according to officials and human rights groups.
Evidence of torture, malnutrition and medical neglect has emerged from autopsies and witness accounts, raising suspicions of systematic abuse in Russian detention facilities.
Bodies returned to Ukraine are often badly mutilated or decomposed, prompting concerns about attempts to conceal war crimes.
While Russia has accused Ukraine of mistreating POWs, the United Nations says such cases are significantly less frequent and severe.
One victim, Serhii Hryhoriev, was officially said to have died of a stroke, but a Ukrainian autopsy and testimony from a fellow detainee suggest he suffered violent abuse.