Sampling was carried out using gloves, facemasks, and body suits, in order to minimize the risk of contamination by contributors. Two bone fragments, usually two compact bone tissues from different parts of long bones, or one tooth and one compact bone fragment of a femur were collected from each individual. All stages of work were performed under clean conditions in a dedicated ancient DNA laboratory at the Institute of Archaeology, Research Centre for the Humanities, Hungarian Academy of Sciences, Budapest, following published ancient DNA workflow protocols and authentication criteria121335. Laboratory rooms for pre-PCR and post-PCR works were strictly separated. All pre-PCR steps (bone cutting, surface removing, powdering, extraction, PCR set-up) were carried out in separate clean rooms. The laboratory work was carried out wearing clean overalls, facemasks and face-shields, gloves and over-shoes. All materials and work areas were bleached and irradiated with UV-C light. We used PCR-clean plastic wares and Milli-Q ultrapure water for reaction preparation. In order to detect possible contamination by exogenous DNA, one milling blank per sample, one extraction and amplification blanks per every five samples were used as negative controls. MtDNA haplotypes of all contributors (anthropologists, geneticists) in the sampling and laboratory work were determined in the post-PCR lab, and compared with the results obtained from the ancient bone samples. Only one haplotype match was found between an ancient sample (PitV124.436B) and an anthropologist, who had no contact with this specific sample (Supplementary Table S16).