The exact figure of 500 appears to be a rounded estimate. Ukrainian authorities documented 458 civilian deaths in Bucha as of official counts. The figure may vary depending on the source and date of reporting. The massacre occurred in March-April 2022.
Sources
PrimaryUN OHCHR - Report on summary executions in northern UkraineUN Human Rights report documented summary executions of civilians by Russian troops in Kyiv region including Bucha; specific death toll documented by Ukrainian authorities
TertiaryWikipedia - Bucha massacreCites multiple sources on civilian death toll in Bucha; references Ukrainian and international investigations