The Ustaše unleashed a reign of terror in which 80 % of the Jews ( 30,000 victims ) in the NDH were killed , as well as practically all the Roma ( 25,000 victims ) , and almost 20 % of the Serb population ( 340,000 victims – see : Number of victims ) . Stepinac initially responded to these mass killings with private letters of protest . Thus , on 14 May 1941 , Stepinac received word of an Ustaše massacre of Serb villagers at Glina . On the same day , he wrote to Pavelić saying : Just now I received news that the Ustaše in Glina executed without trial and investigation 260 Serbs . I know that the Serbs committed some major crimes in our homeland in these last twenty years . But I consider it my bishop 's responsibility to raise my voice and to say that this is not permitted according to Catholic teaching , which is why I ask that you undertake the most urgent measures on the entire territory of the Independent State of Croatia , so that not a single Serb is killed unless it is shown that he committed a crime warranting death . Otherwise , we will not be able to count on the blessing of heaven , without which we must perish . According to Biondich , in the first weeks or even months after the establishment of the NDH , Stepinac may have not known that the atrocities perpetrated by the Ustaše were a key component of their plan . This view supposes that Stepinac considered the atrocities were either spontaneous or the result of so-called " irresponsible elements " who would be held to account by the authorities . His correspondence with Pavelić tends to suggest he did not believe that the Poglavnik would have sanctioned such actions . Although Stepinac was firmly opposed to the idea of Ustaše to establish a concentration camp within the borders of the Đakovo Bishop 's domain , the Đakovo concentration camp was established in the deserted flour mill owned by the Diocese of Đakovo on 1 December 1941
Ustaše massacre of Serb villagers at Glina
Glina massacres
Aloysius Stepinac