The first investigation at the Jasenovac concentration camp – Camp III Ciglana, in Donja Gradina, was carried out by the District Commission for Determining Crimes of Occupiers and Their Collaborators from Nova Gradiška on 11 May 1945. After having inspected the camp area, the Commission crossed the Sava River. They found ashes and remains of burnt bones, including nine oil barrels, on meadows in Donja Gradina where earth had been freshly dug up. The ash traces stretched all the way to the Sava River bank. The Inquiry Commission of the State Commission of Croatia for Determining Crimes of Occupiers and Their Collaborators arrived in Jasenovac on 18 May 1945. One month later, this Commission revisited the area of the former camp. Surviving prisoners, who participated in the breakout, provided the Commission with information on the appearance, work organization, everyday life and the last days of the camp. During such investigations, a certain number of photos were taken showing the condition of former camp’s buildings, corpses and skeletons of prisoners in the camp, on the Sava River bank and in the river itself.

In its study, published in 1946, the Commission stated that the exact number of victims in the Jasenovac camps could not be determined, but that the number could be between 500,000 and 600,000.