Joseph Mengele who experimented on adults and children in the Auschwitz death camps. He was a prime target and was, for many years, the world's most wanted criminal. The Hunters were Simon Wiesenthal, the UN War Crimes Commission and even Mossad. But none of them succeeded. Wiesenthal lacked the resources. The official investigators made blunders, twice letting Mengele slip through their hands. Mossad preferred to concentrate on Eichmann. After the war, the victorious powers had literally millions of POWs to screen. Among them were 22 people called Josef Mengele. So even though the hunt was one for the "Angel of death" of Auschwitz, he simply got lost in an American POW camp. Once out, Mengele was simply able to slip out of view thanks to the Nazi escape organisation, Odessa. But one man would not give up on him. Simon Wiesenthal had been imprisoned in concentration camps twice during the war, but managed to get out of the first through a degree of collaboration. He was re-captured after a year and survived because his new guards needed prisoners in order to escape being sent to fight on the Eastern Front.