In 2015, Flemish journalist Jeroen de Bruyn and Joop van Wijk, Bep Voskuijl's youngest son, wrote a biography, Bep Voskuijl, het zwijgen voorbij: een biografie van de jongste helper van het Achterhuis (Bep Voskuijl, the Silence is Over: A Biography of the Youngest Helper of the Secret Annex), in which they alleged that Bep's younger sister Nelly (1923–2001) could have betrayed the Frank family. According to the book, Bep's sister Diny and her fiancé Bertus Hulsman recollected Nelly telephoning the Gestapo on the morning of 4 August 1944.[42][43] Nelly had been critical of Bep and their father, Johannes Voskuijl, helping the Jews. (Johannes was the one who constructed the bookcase covering the entrance to the hiding place.)[44] Nelly was a Nazi collaborator between the ages of 19 and 23.[45] Karl Silberbauer, the SS officer who received the phone call and made the arrest, was documented to say that the informer had "the voice of a young woman".[43]
The camps were liberated by the Allied forces between 1944 and 1945. The first major camp, Majdanek, was discovered by the advancing Soviets on July 23, 1944. Auschwitz was liberated, also by the Soviets, on January 27, 1945; Buchenwald by the Americans on April 11; Bergen-Belsen by the British on April 15; Dachau by the Americans on April 29; Ravensbrück by the Soviets on the same day; Mauthausen by the Americans on May 5; and Theresienstadt by the Soviets on May 8.[42] Treblinka, Sobibór, and Bełżec were never liberated, but were destroyed by the Nazis in 1943. Colonel William W. Quinn of the U.S. 7th Army said of Dachau: "There our troops found sights, sounds, and stenches horrible beyond belief, cruelties so enormous as to be incomprehensible to the normal mind."[43][44]

The crematoria consisted of a dressing room, gas chamber, and furnace room. In crematoria II and III, the dressing room and gas chamber were underground; in IV and V, they were on the ground floor. The dressing room had numbered hooks on the wall to hang clothes. In crematorium II, there was also a dissection room (Sezierraum).[172] SS officers told the victims they were to take a shower and undergo delousing. The victims undressed in the dressing room and walked into the gas chamber, which was disguised as a shower facility; signs in German said "To the baths" and "To disinfection". Some inmates were even given soap and a towel.[173]

Use of the word "concentration" came from the idea of confining people in one place because they belong to a group that is considered undesirable in some way. The term itself originated in 1897 when the "reconcentration camps" were set up in Cuba by General Valeriano Weyler. In the past, the U.S. government had used concentration camps against Native Americans and the British had also used them during the Second Boer War. Between 1904 and 1908, the Schutztruppe of the Imperial German Army operated concentration camps in German South-West Africa (now Namibia) as part of its genocide of the Herero and Namaqua peoples. The Shark Island Concentration Camp in Lüderitz was the largest camp and the one with the harshest conditions.