STORY: Russian forces entered the village of Bohdanivka, about 30 miles northeast of the Ukrainian capital, on March 8 and set up a base in the school, which they later set on fire, Ukraine's Prosecutor General Iryna Venediktova said.
Ukraine says Russian troops murdered, raped and tortured villagers in Bohdanivka and other areas near Kyiv.
Russia denies targeting civilians in its "special military operation" to disarm and "denazify" Ukraine. Kyiv and its allies say the invasion is an unprovoked war of aggression.
British lawyer Wayne Jordash, who is coordinating mobile justice teams that will assist the Ukrainian investigators, said the probes would "go to the top" of Russia's political and military leadership.
The advisory group was established last month to coordinate international support for Ukrainian investigators who have received about 17,000 reports of potential war crimes since Russian President Vladimir Putin ordered the February 24 invasion of Ukraine, Williamson said.