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.

They called him “The Hangman”. Reinhardt Heydrich, became one ofthe most hated men in all of occupied Europe. He was the real mastermind behind the “Final Solution” and created the blueprint for the Holocaust. Heydrich’s ambition knew no bounds, he even wanted to replace Adolf Hitler. He ruled occupied Czechoslovakia with a rod of iron and thought himself untouchable. But in London, a top-secret hit squad had different ideas. They began to target Heydrich for execution…

Commander-in-chief of the Luftwaffe, Hermann Goering was Hitler’s anointed successor and had been at the Fuhrer’s side for over twenty long years. Goering also first suggested the idea of a “Final Solution” - the extermination of the Jews. At the end of World War 2, Goering was the only top Nazi left alive. As the Allies closed in, one after the other, top Nazis had chosen suicide. Hitler, Goebbels, Himmler, all gone. Hermann Goering was the last man standing and the Allies were desperate to put him in the dock. He was soon apprehended and any idea of a happy ending rapidly vanished. At the trial of the century in Nuremberg, he became the “Star exhibit”, his guilt, “unique in its enormity”… However the outcome would be as mysterious as it was controversial and would take everyone by surprise.

Martin Bormann was vital to Hitler. Bormann made Hitler, and the Third Reich, rich through thinly veiled extortion schemes such as The Hitler Endowment Fund of German Industry. He also came up with the idea of charging royalties on Hitler's image on postage stamps - and so made his Fuhrer personally wealthy. He became so close to Hitler and the running of the war that Hitler once screamed "To win this war, I need Bormann!". More sinister was Bormann's involvement in ensuring the progress of the final solution . Himmler had to report back to Bormann on the extermination of the Jews.Bormann, Hitler's doctor Stumpfegger and Artur Axmann (the Head of the Hitler Youth) all left the bunker in Berlin together after Hitler's suicide on 30th April 1945. After Axmann left them at the Lehrter Station Bormann and Stumpfegger disappeared. This led to one of the longest Nazi hunts in history.

Franz Stangl was the Nazi commandant of the Treblinka and Sobibor death camps in Poland. He was responsible for the extermination of around 900,000 men, women and children. At the end of the war, he escaped to Italy where he joined a "rat-line" organised by Vatican officials. From there, he disappeared. Simon Wiesenthal was a survivor of the Holocaust. Born in the Ukraine in 1908, he was rounded up with his family in 1939 and imprisoned in a labour camp where he serviced the German railroad. In May 1945, he was liberated by Allied soldiers from Mauthausen camp. His six-foot-frame weighed barely 99 pounds. Restored to health, he vowed to track down some of the Nazi monsters who had put him and so many other Jews through hell.

Two weeks after the end of World War II Heinrich Himmler, head of the SS and the Gestapo – Germany’s dreaded secret police, killed himself while being interrogated by the British. On the face of it his death looked like straightforward suicide.As the mastermind behind the Final Solution, the systematic murder of six million Jews, no-one mourned Himmler’s passing. However it was not long before rumours about the way in which Himmler died began to spread, lasting for years to come.

Adolf Eichmann - The logistical brains behind Hitler’s Final Solution. He organised the transportation and incarceration of 6 million Jews to the death camps. The Holocaust even made him rich. Eichmann stole the jews’ last possessions and sold them for profit. At the end of the war, when others were being arrested, Adolf Eichmann vanished. He had escaped to Argentina where he thought he was safe, but on his tail was Israel’s ruthless intelligence agency…Mossad.

These stories of pursuit and the struggle to balance the scales of justice are full of drama and tragedy. Brilliant German scientists worked for the Nazi regime in the 1930s and 1940s, creating the V2 ballistic missile. When the war ended, the US was desperate to get its hands on these scientists before the Russians did. They wanted their expertise as the need for military superiority overrode any concerns of bringing these criminals to justice. Their wartime work hid a dark secret. Hundreds of slave labourers died building the V2. There was a chase across Germany in 1945 to get them before the Russians did. But these rocket scientists had blood on their hands.

Former Gestapo officers in Eastern France, Hans-Dietrich Ernst and Heinrich Neuchtschwanger. Also targeted, the evil Dr Rohde, who executed four female spies by lethal injection. Ernst and Neuchtschwanger murdered some 31 SAS soldiers caught during a secret mission, Operation Loyton. The SAS War Crimes Investigation Team, commanded by Major Eric Alistair 'Bill' Barkworth. SAS secretly hunted down these Gestapo officers. It is said that the SAS always prefer to 'hunt their fox in secret' - and this is what they did here. Alongside him was SOE operative, Vera Atkins There were 31 missing SAS men, victims of the botched Operation Loyton. But there were no clues. No bodies. They had just disappeared. It smelled bad.

Speer's crimes included using and organising slave labour in death camps and prolonging the war by his fanatical work to develop the Nazi war machine. He was hunted by two groups. The UN War Crimes Commission, but first he was wanted by the US Strategic Bombing Survey. This strange group of people included the economist JK Galbraith and the veteran arms negotiator Paul Nitze. These were hardly hardened prosecutors and they had authorisation from the highest level to keep Speer out of the hands of the Criminal Investigators from the UN. They tracked Speer down and spirited him away to a country house after the war, where he was extensively questioned, giving the Americans detailed information about the effectiveness of US bombing. This was critical intelligence and would eventually shape much of US strategy during the Cold War. When this story leaked out it caused huge controversy as the hint has always been that the Americans agreed to go easy on Speer at his trial in exchange for his co-operation.

1987 was a dramatic year for Nazi Hunters. Klaus Barbie in France and John Demjanjuk in Israel were about to face justice, 45 years after their alleged war crimes. Why had it taken so long?

Joachim Peiper and his vicious bunch of SS thugs marched US 285th Field Artillery Observation Battalion into a field near Malmedy in January 1945 and shot them. There were a series of other massacres of US soldiers which were attributed to Peiper. The hunters were members of Supreme Headquarters Allied Expeditionary Force. They were horrified by the brutality of the action. It was also the biggest massacre of US soldiers in the Second World War and caused uproar among the US public.

The story of the Jewish Avengers after the Second World War has been rarely told. For the first time, a group of men and women, now in their 80s, tell the extraordinary story of how some Jews decided after the war had ended to seek brutal and shocking “eye for an eye” revenge on the Germans. They believed that those who’d delivered the holocaust had simply not paid a high enough price.