EDS NOTE: GRAPHIC CONTENT - A burned out body of Ukrainian military prisoner is seen in destroyed barrack at a prison in Olenivka, in an area controlled by Russian-backed separatist forces, eastern Ukraine, Friday, July 29, 2022. Russia and Ukraine accused each other Friday of shelling the prison in Olenivka in a separatist region of eastern Ukraine, an attack that reportedly killed dozens of Ukrainian military prisoners who were captured after the fall of a southern port city of Mariupol in May. (AP Photo)

EDS NOTE: GRAPHIC CONTENT - Investigators examine bodies of Ukrainian military prisoners at a prison in Olenivka, in an area controlled by Russian-backed separatist forces, eastern Ukraine, Friday, July 29, 2022. Russia and Ukraine accused each other Friday of shelling a prison in Olenivka, a separatist region of eastern Ukraine, an attack that reportedly killed dozens of Ukrainian prisoners of war who were captured after the fall of a southern port city of Mariupol in May. (AP Photo)

A soldier stand guard next to a wall of a prison in Olenivka, in an area controlled by Russian-backed separatist forces, eastern Ukraine, Friday, July 29, 2022. Russia and Ukraine accused each other Friday of shelling a prison in a separatist region of eastern Ukraine, an attack that reportedly killed dozens of Ukrainian military prisoners who were captured after the fall of a southern port city of Mariupol in May. (AP Photo)

In this photo taken from video a view of a destroyed barrack at a prison in Olenivka, in an area controlled by Russian-backed separatist forces, eastern Ukraine, Friday, July 29, 2022. Russia and Ukraine accused each other Friday of shelling a prison in a separatist region of eastern Ukraine, an attack that reportedly killed dozens of Ukrainian military prisoners who were captured after the fall of a southern port city of Mariupol in May. (AP Photo)

In this photo taken from video a view of a destroyed barrack at a prison in Olenivka, in an area controlled by Russian-backed separatist forces, eastern Ukraine, Friday, July 29, 2022. Russia and Ukraine accused each other Friday of shelling a prison in a separatist region of eastern Ukraine, an attack that reportedly killed dozens of Ukrainian military prisoners who were captured after the fall of a southern port city of Mariupol in May. (AP Photo)

EDS NOTE: GRAPHIC CONTENT - In this photo taken from video a view of destroyed barrack at a prison in Olenivka, in an area controlled by Russian-backed separatist forces, eastern Ukraine, Friday, July 29, 2022. Russia and Ukraine accused each other Friday of shelling a prison in a separatist region of eastern Ukraine, an attack that reportedly killed dozens of Ukrainian military prisoners who were captured after the fall of a southern port city of Mariupol in May. (AP Photo)

Investigators put fragments on display of what they say were rickets fired from U.S.-supplied HIMARS systems near a destroyed barrack at a prison in Olenivka, in an area controlled by Russian-backed separatist forces, eastern Ukraine, Friday, July 29, 2022. Moscow opened a probe into the attack, sending a team to the site from Russia's Investigative Committee, the country's main criminal investigation agency. The state RIA Novosti agency reported that fragments of U.S.-supplied precision High Mobility Artillery Rocket System rockets were found at the site. (AP Photo)

Investigators put fragments on display of what they say were rickets fired from U.S.-supplied HIMARS systems near a destroyed barrack at a prison in Olenivka, in an area controlled by Russian-backed separatist forces, eastern Ukraine, Friday, July 29, 2022. Moscow opened a probe into the attack, sending a team to the site from Russia's Investigative Committee, the country's main criminal investigation agency. The state RIA Novosti agency reported that fragments of U.S.-supplied precision High Mobility Artillery Rocket System rockets were found at the site. (AP Photo)

This handout picture released by the Russian Investigative Committee on July 29, 2022 shows what is said is the destroyed detention centre in the settlement of Olenivka in the separatist-held region of Donetsk. - Russia and Moscow-backed separatists on July 29, 2022 accused Kyiv's forces of striking a jail holding Ukrainian prisoners of war in eastern Ukraine, saying dozens of people died and scores were wounded. (Photo by Handout / Investigative Committee of Russia / AFP) / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT "AFP PHOTO / Russian Investigative Committee / handout" - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS