A few weeks later Yugoslavia collapsed and on April 19, 1941, the prison was taken over by authorities of the newly formed Independent State of Croatia. Prisoners were segregated based on ethnicity, with the camp split into "Serbian-Yugoslav", "Jewish" and "Communist" sections. Following German invasion of USSR, the Yugoslav Communist Party started a resistance movement that would become known as the Partisans. The Ustaša regime decided to retaliate by killing some of Kerestinec prisoners.