Other controversial evidence included Demjanjuk's tattoo. Demjanjuk admitted the scar under his armpit was an SS blood group tattoo, which he removed after the war, as did many SS men to avoid summary execution by the Soviets. The blood group tattoo was applied by army medics and used by combat personnel in the Waffen-SS and its foreign volunteers and conscripts because they were likely to need blood or give transfusions. There is no evidence that POWs trained as police auxiliaries at Trawniki were required to receive such tattoos, although it was an option for those that volunteered.