(Reuters) – Ukraine has launched a Book of Executioners, a system that collects evidence of war crimes Kyiv claims were committed under Russian occupation. President Volodymyr Zeleskiy announced Tuesday.

Ukrainian authorities claim they have filed more than 12,000 cases of alleged war crime involving 600 people since Feb. 24, the Kremlin’s offensive.

Zelenskiy spoke in a video message that “Next week, an exclusive publication will be launched – ‘The Book of Executioners’ – an information systems to collect data confirmations about war criminals, crimes from the Russian arm,” Zelenskiy explained.

According to Zelenskiy, this will be one of the key elements in his ongoing pledge to have Russian servicemen held accountable for their crimes against humanity that have been described by Ukrainian authorities as murders.

Zelenskiy declared, “These are concrete facts concerning concrete individuals guilty in concrete cruel crimes against Ukrainians.”

He also referred to Bucha, a Kyiv suburb. Investigators discovered evidence that there were mass executions.

Russia claimed that it did everything possible to protect civilians from being targeted in the “special military operation” against Ukraine. Russian officials dismissed Bucha’s events as “fabrications” by Ukrainian authorities, after Russian forces had left Bucha in March.