There was a reason for that. Killing Cossacks wasn't just a one-off.
https://www.lemonde.fr/en/international/article/2023/01/12/stepan-bandera-the-ukrainian-anti-hero-glorified-following-the-russian-invasion_6011401_4.html#
https://www.britannica.com/biography/Stepan-Bandera
https://www.imdb.com/title/tt0087553/