The first limited research in the Jasenovac concentration camp, was conducted on May 11, 1945 by the District Commission for the Crimes of Occupiers and their Assistants from Nova Gradiška.
The State Commission of the Republic of Croatia for the Investigation of War Crimes of Occupiers and their Assistants determined on May 18, 1945 the number killed in Jasenovac ranged from about 500.000 to 600.000 but that the exact number of victims in the Jasenovac concentration camp could never be accurately determined.
The first panoramic aerial film of the Jasenovac concentration camp was made in 1945. Footage covered the northern part of the camp. However, film footage of Donja Gradina has not been found.
The Yugoslav Air Force recorded the flow of the Sava River in 1946; however, the negatives that covered most of Donja Gradina also have not been found.
Nikola Nikolić, a former inmate at Jasenovac, and his son Sergij did research in 1947 in Donja Gradina and found 248 clearly visible mass graves whose dimensions were 60-80 m long, 6 m wide, and 4 m deep. On the right bank of the Sava River, Nikolić discovered two wagons full of ashes, burned skulls and vertebrae that had been thrown away there after the corpses were burned at Donja Gradina.
The first photogrammetric records were made by The Institute of Photogrammetry in Belgrade in 1957.
Research conducted in 1961.
On March 15, 1961, The Federal Association of National Liberation War Veterans (SUBNOR) of Bosanska Dubica discovered three mass graves.
During the first excavations, 17 human skulls were found in one square meter. Skulls were fractured and broken up, which indicates that the victims were killed with a dull-hard object (mallet). The limb bones were also broken. This is because the graves were rolled over with heavy equipment.
At the second excavation, boiled bones were found, and in the third one burned remains of the victims. In addition to the skeletons, personal belongings of the victims such as clothes, shoes, pots, etc. were also found. Personal items indicate that these people were not prisoners (because they would have been previously undressed and robbed) but were brought directly from their homes. They mostly carried kitchen items (pots, cups, knives, spoons, forks, etc.), personal hygiene items (mirrors, toothbrushes, combs, etc.), and in addition to clothing, personal jewelry and sometimes even ducats and money were found.
Research conducted between 1963. and 1965.
In the period from 1963 to 1965, multidisciplinary excavations were organized in Donja Gradina. Some grave pits were visible: darker areas of grass above the remains of the victims. But many of the graves could not be seen because the residents of the village of Donja Gradina were allowed to cultivate the land for agricultural purposes. Because of the inability to identify the upper surface of the grave pits by ordinary observation of cultivated land, the ground was bored with a “Dutch drill.” This drilling was done by Alojz Šercelj. He found undiscovered burial pits and identified directions and lengths of all the discovered graves. Geodesists from Bosanska Dubica in 1964 drew the outline of each grave on the ground surface of Donja Gradina.
Before 1964, historiography had not used the results of anthropological research. Anthropological research began with probe excavations on the 9th and was finished on April 17, 1964. Overall, 100 graves were probed with 130 boreholes.
This research identified three types of graves in Donja Gradina:
- graves of people murdered in a standing position,
- graves where corpses had been transported for burial and
- graves containing the boiled bones of the victims, who had been boiled in iron caldrons in Donja Gradina, together with burned bones.
These types of graves demonstrate that there were mass murders in Donja Gradina, that Ustashas made soap out of humans, and that the posthumous remains were excavated and burned, and, moreover, that living people were set on fire. Researchers defined the number of skeletons per cubic meter in the mass graves of Donja Gradina: 17-25 skeleton/m³. Remains of the victims in most cases lay in disarray, one over the other, intertwined with each other in different positions and levels. They lay in the way they had fallen into the pit. All the circumstances indicate that they were killed from the edge of the grave.
Social and ethnic identity of the victims was determined by personal and everyday objects found with the skeletons in mass graves. The remains of clothes, shoes, jewelry and other everyday objects indicated whether the victims were of rural (rubber shoes, rubber boots) or urban origin.
Gender was determined according to classical anthropological methods. For poorly-preserved skeletons remains of hair (hair length, the remains of women’s braids and children pigtails) helped determine the gender. Hair was almost always preserved and remained on the skull bones.
Human skeletons were excavated from the graves and, after the anthropological research, were buried at the same place. All items found in the graves were also re-buried after analysis and registration, except for a certain number of skulls with injuries that indicated the cause of death. These were turned over to the museum at Jasenovac. Some of the excavated items were also handed over to the museum: gold coins, jewelry, wedding rings, gold teeth, etc. The brain remains found in the skulls were sent to the Institute of Forensic Medicine in Ljubljana for further investigation.
Research conducted between 1973. and 1976.
In 1973, the Military-Geographic Institute completed recordings for a topographic map at a scale of 1:9.000. It was filmed with color technology. The map covers 240 km² from Kostajnica to Stara Gradiška, the area of the left and right banks of the Sava River, as well as left and right banks of the Una River to Hrvatska and Bosanska Kostajnica. The whole project was organized by the INA Project from Zagreb, headed by Dr Marinko Olujić.
The Geodesy Institute of the Republic of Slovenia in Ljubljana conducted an aerial survey of Donja Gradina and the wider area of Jasenovac in 1976. They used multi-emulsion techniques. With this, researchers discovered an area of 13.425 m² with more possibility and an area of 27.340 m² with less possibility of grave presence. The area of registered and discovered graves is about 10.000 m². After the identification of suspicious areas, they started the process of probing in the period from August 25th to September 5th of 1976. They bored more than 1.000 holes. This research was continued at first because previous studies had indicated the possibility of discovering new mass graves and also because it could contribute to better understanding of the arrangement of Donja Gradina.
Researchers drilled with a hand auger to a maximum depth of 250 cm. Sites that were suspicious according to drilling results were opened at first with an excavation of 1×1 m dimensions. Later the hole was expanded in the direction of the bones and other remains. In this way, about 50 m² of graves in four places were uncovered. Discovered remains were analyzed and submitted for the anthropological report.
Advanced research of excavated skeletons revealed different types of injuries. Usually, these were depressions on the skull at the back or on the temples. Firearm murders were rare in this area.
Regarding age of the victims, in the anthropological research of 1976 the younger age groups dominated, and there were many children.
In several excavations of the surface, completely softened bones were extracted. The conclusion of anthropologists is that these bones were boiled. Evidence of this was steel cauldrons (12 of them) that were found after the liberation of Jasenovac. In these cauldrons, traces of several chemicals and soda were found.
Research conducted in 1986.
In November 1986, the Department of Forensic Medicine and Criminology at the Faculty of Medicine, University in Zagreb examined the skeletal remains of at least 152 people. This osteological material was found in an uncovered grave in Donja Gradina. The analysis determined that out of 152 people, 37 were male, 51 female, and 11 children, while in 53 cases sex could not be determined. Eighty six were determined to be young adults, 15 middle-aged people, 12 elderly people, 11 children, while in 28 cases, the age could not be determined.
Among the skulls, there was one skull that was fully preserved, and as a result of a special postmortem process (Saponification), the brain was fully preserved. On the crown part of the occipital bone an irregular defect was discovered.
Bleeding was found in the brain and the cerebral ventricles, and traces of very heavy bleeding were found between the bones of the right arch of the skull and brain. This bleeding was caused by a compression of the brain, which, in fact constituted the immediate cause of death. The person to whom the skull belonged suffered injury from a blow with a dull, hard object to the crown part of the occipital bone. According to the amount of bleeding between the bones of the right side of the skull and the brain, it can be determined with certainty that the person lived after the injury for some time, at least 2-5 hours. In this case it was a young woman.
Research conducted in 1991.
The Regulation Program of 1977 established 43 examination fields in the narrow area of the Donja Gradina Memorial Site. The fields were organized according to their layout and boundary lines drawn of a narrow planning zone on the west and south side of the complex.
Indication of suspicious areas were obtained from the testimonies of local people, the records of the committee investigations immediately after the war and aerial photogrammetric photos from 1976. Suspicious areas were highlighted for research in the form of investigative fields. Probing and excavation tests of suspected areas were used in identification of the graves.
In 1990 and 1991, 11 examination fields were researched. At the second investigation site of examination field IP-6, 26 mass graves were found. This site was therefore selected for further excavation planning.
Research conducted in 1993.
In March of 1993, a British ITN television crew, led by Clive Gordon, visited Donja Gradina. At his suggestion and by a random sample method, one grave at the grave field “Topola” (near the soap factory) was opened.
Mainly osteological remains of feet, hands, forearms and lower legs were found. It was obvious that inmate bodies were cut here for soap production. Since that time, this grave is called the “Cutting Grave”.
According to the gathered data and statements of two local residents of Donja Gradina, Branko Đ. Vukić and Vaso Rokić, one previously unknown and unregistered mass grave on the “Livadak” tract was discovered.
Removal of shrubs and weeds started in April of 1993. A depression showed up. Based on the compactness of the soil, the composition of this depression and the surrounding land, it was established that there had been no previous excavation. The grave was drilled with a hand probe. Already at a 60 cm depth, the probe scraped and bounced, an early sign that the first borehole was positive. They began opening the grave. It was opened to its full-width and to a length of 1.5 m. At this depth, a piece of nylon foil was found.
Villagers from Gradina explained the secret of nylon grave. In 1966 the grave was discovered in one of the scrubs in Gradina. Remains of 30 individuals, 29 men and one woman, aged 18-20 years, were found in the grave. The remains of clothing and footwear revealed that these young men and woman originated from the Kozara Mountain area and were of Serbian nationality. Crushed skulls indicated they were murdered by blows to the head with dull, hard objects, which was one of the main methods of liquidation of Ustasha victims at Jasenovac.
After processing the osteological material, the bones were wrapped in nylon film and re-buried at the new location.