After receiving tip-offs, German prosecutors were recently granted access to secret files in Brazil and Chile that confirmed the true number of Third Reich immigrants.
According to the documents, an estimated 9,000 war criminals escaped to South America, including Croatians, Ukrainians, Russians and other western Europeans who aided the Nazi murder machine.
War criminals: Secret files have revealed that an estimated 9,000 Nazis, including Holocaust mastermind Adolf Eichmann (left) and Auschwitz doctor Josef Mengele (right), fled to South America in the aftermath of the Second World War
Most, perhaps as many as 5,000, went to Argentina; between 1,500 and 2,000 are thought to have made it to Brazil; around 500 to 1,000 to Chile; and the rest to Paraguay and Uruguay.
These numbers do not include several hundred more who fled to the safety of right-wing regimes in the Middle East.
Previous estimates as to how many Nazis fled to South America have varied wildly from 5,000 to 300,000.
The files also showed that during the war Argentine President General Juan Peron sold 10,000 blank Argentine passports to ODESSA – the organisation set up to protect former SS men in the event of defeat.
Kurt Schrimm, 62, head of the central war criminal authority in Germany, is among the legal team sifting through archives.
He said: 'These documents provide the hottest leads we have had for years.'
Mr Schrimm said a female historian provided the clues about the Nazis who got away, who included Holocaust mastermind Adolf Eichmann, Auschwitz doctor Josef Mengele and Treblinka death camp commander Franz Stangl.
During the war, Argentinian President Juan Peron, pictured with his wife Eva in Buenos Aires in 1950, sold 10,000 blank Argentine passports to ODESSA - the organisation set up to protect former SS men in the event of defeat
THE LEADING NAZIS WHO FLED TO SOUTH AMERICA
Adolf Eichmann hid under the alias of Ricardo Klement in Argentina as early as 1952. He raised his family and worked in a car plant.
During the war, Eichmann was the right-hand-man to SS chief Heinrich Himmler in the Third Reich - who was responsible for the trains that carried millions to their deaths at extermination camps in Nazi occupied Poland. Eichmann was hanged in Israel in 1962.
Josef Mengele was known for his horrific genetic experiments in concentration camps including the dissection of live babies and injecting dye into the eyes of prisoners. He hid out in Argentina until his death in 1979.
Several others escaped to Chile. Walter Rauff a high-ranking SS officer who invented the 'Death Trucks' - with which 500,000 prisoners were murdered with lethal gas at Auschwitz - arrived in South America in 1950. He spent a short amount of time in jail and died in Santiago in 1984.
Paul Schaeffer began his career in the Hitler Youth before rising through the ranks and arrived in Chile in 1960. He was a known paedophile but was not locked up by Chilean authorities until 1996. He died in 2010.
There is also the hope that the mountain of documents may throw up a living fugitive.
But Mr Schrimm added: 'Each day that passes makes that less and less likely but I do not want people to say in the future that we did not try.'
Mr Schrimm and his colleague Uwe Steintz, 52, believe the archives may also provide clues to Nazis who sneaked back to the Fatherland to live out their days undetected.
Of particular interest to the hunters are details of the so-called 'rat lines' - the escape routes out of a shattered Europe after WW2 that allowed an estimated 800 murderers to escape on passports provided by the Vatican.
Since arriving in South America three weeks ago, Mr Schrimm and Mr Steintz have pored over the Arquivo Historico records in Rio de Janiero.
The Archivo Nacional is the repository for all immigration documents.
They show that 20,000 Germans settled in Brazil alone between 1945 and 1959.
Mr Schrimm said: 'Many are under a false name with a dark past.'
Many South American countries postwar were ruled by fascist-style military dictatorships that welcomed the brutal servants of Nazism with few questions asked.
Mr Steintz said: 'Already we see something of a pattern in the way these criminals operated. They almost always entered the country alone and sent for their families afterwards.
'And most entered on a passport of the International Red Cross. Eight hundred higher functionaries of the SS and Nazi state entered Argentina alone on such passports.'
The files show that the contact point for many was German Bishop Alois Hudal, priest-confessor to the German Catholic community in Rome.
Investigators hope that the files will yield up cross references to the secret services of Chile and Brazil detailing names of intelligence agents who helped the Nazi war criminals.