In the last three years, as part of the Vatican Archives Initiative (VAI), I have been surveying the Ruteni/Ruthenians collection in the archive of the Dicastery for the Eastern Churches (ACO). The first part of my talk provides insight into major themes of Holocaust research that appear consistently in the ACO/Ruthenians collection, including: 1) the increasing inter-ethnic and inter-religious violence in East Central Europe before World War II. This culture of violence, normalization of abusive behaviour, and murder made later violence and murder of Jews more acceptable; 2) conversion of Jews to Christianity during the Holocaust and the larger context of forced conversions/changes of rites, which were generally driven by ethnic divisions and border changes; 3) collaboration of Ruthenian/Ukrainian Greek Catholics with local Nazi-like organizations and their participation in the creation, in spring 1943, of Waffen SS Galicia Division; 4) the role of the Holy See in helping war criminals, including in the support and relocation of 10,000 Waffen SS Galicia POWs; 5) Catholic rescue and its controversies, especially in relation to hiding of Jewish children. Towards the end of my presentation, I will focus on two specific documents to showcase how material in the Pope Pius XII collections enhances current historiography. The first is a December 1942 letter by Andrey Sheptytsky, Greek Catholic Metropolitan of Galicia, providing details about Jews' persecution and murder. The letter was discussed in an audience with Pope Pius XII, and my talk will provide insight on that. The second, is a February 1942 letter sent to Adolf Hitler by Metropolitan Sheptytsky and other Ukrainian national leaders, including the head of OUN-M, Andriy Melnyk. In current historiography there is a supposition that in February 1942 Mons. Sheptytsky wrote to Heinrich Himmler. As I will argue, it is likely that this letter to Hitler is the one supposed to have been sent to Himmler.