The diaries of Nazi doctor Josef Rudolf Mengele, also known as the 'Angel of Death' for his murderous acts at the Auschwitz concentration camp during World War 2, will be auctioned in the United States on Thursday. The diaries have been obtained by the Alexander Historic Auctions company of Stamford, Connecticut. This manuscript was sold to the company by an anonymous client. The writings are comprised of autobiographical chapters, diaries, stories, intense philosophical introspections and debates, direct quotations of conversations, political commentary, history, and poetry. Upwards of 95 percent of the material in this archive is unpublished, according to the company. Before joining the Nazi party, Mengele earned doctorates in anthropology from Munich University and in medicine from Frankfurt University. He began his military career as an SS officer and ended up as chief physician in the Auschwitz-Birkenau camp. Initially Mengele was known for being one of the SS physicians who supervised the selection of prisoners who arrived at the camp. It was Mengele who determined who was to be sent to the gas chambers, and who was to be a laborer. He later gained notoriety for performing grisly human experiments on camp inmates, including children. He especially singled out twins for horrific experiments involving their genetic composition. The diaries, which were written between 1960 and 1975, include Mengele's philosophical pondering, autobiographical stories, and songs he wrote while hiding in South America, after fleeing Germany at the end of the war. In most of the texts, Mengele writes in the third person and calls himself "Andreas." In one diary, according to the auction house, he indicated that sexual promiscuity has led "to a dreadful mixing of the races with the northern Europeans... when you start mixing the races, there is a decline in civilization." The diaries contain 3,500 pages written by the elusive doctor, who tortured many prisoners at Auschwitz, including those known as "Mengele's twins". It is estimated that the pages will be sold for somewhere between 300,000 and 400,000 dollars. "Most of the pages are in excellent condition," the spokesman for the Alexander Historic Auctions auction house said. According to the spokesman, the diaries were found by Brazilian police in 2004, at the home of a German couple living in Sao Paulo. The pages were handed over to Mengele's son, Rolf, who it is believed never really knew his father, and met him only on two occasions. Mengele escaped the Red Army, and twice was released from American detention camps when they failed to realize he was a wanted war criminal. After four years in hiding on a farm in southern Germany, his wealthy family bought him the help of former Nazis so he could flee to South America. Mengele drowned in Brazil in 1979.