After the Red Army definitively expelled the Germans from Warsaw in January 1945, the new communist administration continued to run the buildings as a forced labour camp, and then as a prison, until it was closed in 1956.

The camp and adjacent ruins were additionally used by the German administration as a place of execution, the victims being Polish political prisoners, Jews caught on the "Aryan side", and generally people rounded up on the streets of Warsaw.

The theory, refuted by mainstream historians, contends that KL Warschau was an extermination camp operating a giant gas chamber inside a tunnel near Warszawa Zachodnia railroad station and that 200,000 mainly non-Jewish Poles were gassed there.

[14][15] According to Bogusław Kopka, the first person behind the idea of creating a new concentration camp in Warsaw was Heinrich Himmler, head of the Schutzstaffel (SS), who mentioned it in a letter dated 9 October 1942.

[21] His ideas, however, were met with resistance from the military, the police and civil administration of the General Government, as well as from the Reich Ministry of Armaments and War Production and from German companies using Jewish slave labour.

In a letter dated 16 February 1943, Himmler instructed SS-Obergruppenführer Oswald Pohl, head of SS-WVHA, to create a concentration camp in the "Jewish district" and ordered all German-owned private enterprises operating in the Ghetto to be relocated there.

On the same day, Himmler also wrote a letter to SS-Ogruf Friedrich-Wilhelm Krüger, Higher SS and police leader for the General Government, which demanded that the buildings of the deserted ghetto be demolished after the concentration camp was transported to Lublin.

[23] The idea's implementation was marred with numerous difficulties, so when the Germans decided to accelerate the deportations on 19 April, they met strong resistance from the Jews, who began the Warsaw Ghetto Uprising.

SS-Brigadeführer Jürgen Stroop, who led the efforts aimed at quashing the insurgency, proposed on 16 May 1943, the day the uprising came to an end, to convert the Pawiak prison to a concentration camp.

[27] It is suggested that by creating such a camp, the Germans wanted to destroy evidence of the crimes committed during the suppression of the uprising[28] as well as to enrich themselves by the loot that would be collected in the rubble by slave labourers.

After the work is finished the area is to be covered up with earth and a large park is to be planted.Eventually, Pawiak's status as a prison did not change, but the concentration camp was created on nearby Gęsia street, which was also located inside the Ghetto walls.

[40] However, the construction was repeatedly halted due to the recurring typhus epidemic, which decimated the inmate population and forced the camp's administration to quarantine the premises twice (in January and February 1944, see below, and again in April and May).

[42] The number of SS guards was relatively low, as the former ghetto, itself a closed zone, was surrounded by patrolled walls, and due to the fact that the prisoner functionaries were Germans from the initial transport and were thus delegated much more power than was usual for their counterparts in other camps.

[1][43] Leadership positions were occupied by high- and middle-ranking SS members who were pre-war Third Reich citizens (Reichsdeutsche), while the rank-and-file were usually recruited among the Volksdeutsche, mainly from Southeast Europe but also from other areas.

Conversely, the Institute of National Remembrance's report on the investigation of the crimes committed in KL Warschau says that the Politische Abteilung did exist, but it was directly subordinate to the commandant of Sicherheitsdienst and Sicherheitspolizei in Warsaw, instead of being the main department of the camp's administration.

[2][56] The ethnic composition changed substantially in spring 1944, when several trains from Auschwitz delivered c. 3,000 Hungarian Jews (most of whom originally were deported from ghettos in Mukachevo, Uzhhorod, Khust and Tiachiv, then in Hungarian-occupied Carpathian Ruthenia)[51] who became the majority in the Warsaw concentration camp in the last months of its existence.

German constructions companies, including Berlinisches Baugeschäft (Berlin), Willy Keymer (Warsaw), Merckle (Ostrów Wielkopolski), and Ostdeutscher Tiefbau (Naumburg), operated there on contract and benefitted from slave labour provided by the prisoners.

The demolition and salvage work were hard and perilous labor, carried out at a brisk pace with no regard to loss of life of the prisoners, so fatal workplace incidents were commonplace.

[56] In particular, a typhus epidemic in January and February 1944 decreased the prison population by two-thirds,[2][1] though the sanitary situation improved somewhat by the time the leadership was changed and the camp's construction was finished.

Prisoner functionaries, however, were treated differently – they lived in a separate barrack (with the exception of the Blockältester), could wear civilian clothes, bear arms, and were even sometimes allowed to go outside the camp's premises.

[51][81][d] The vast majority of released Jewish prisoners swiftly took part in the uprising, which Gabriel Finder attributes to an informal political group which that prevented the camp's inhabitants from moral deterioration.

Additionally, Theodor Szehinskyj, a former guard who immigrated to the US in the 1950s, had his US citizenship revoked as a federal court in Pennsylvania found in July 2000 that he had lied in his initial visa application about his past in the SS Totenkopf Division, including in the Warsaw concentration camp; the decision was upheld on appeal to the 3rd Circuit.

The Institute of National Remembrance's (IPN) prosecutors inquired about 208 people whom it identified to be staff members of the concentration camp in 2014, but the Ludwigsburg office only sent information about a fraction of them because of staffing issues related to processing the request of this breadth.

[105] In mid-1988, testimony began to emerge suggesting that the concentration camp was also located near Warszawa Zachodnia railway station, more than 3 km (1.9 mi) away from Gęsia Street, and included gas chambers.

[107] According to Jan Żaryn, when the idea of a monument to the victims of the Warsaw concentration camp approached fruition, the interested parties were unable to agree on inscriptions to be placed on it, so Trzcińska requested that the IPN verify which version was correct.

[125] Historian Daniel Blatman, on the other hand, while seeing the hypothesis as "one of numberless stories that Holocaust deniers around the world are posting online", warned against generalising on the Polish society or the governments it brought to power.

[131] Bogusław Kopka says, though, that during his visit to Warsaw in 1959, Richard Nixon, then Vice President of the United States, managed to lay a wreath in front of the main building of the former concentration camp.

[70] Commemoration efforts were renewed in July 2001, when the Sejm, the lower house of the Polish parliament, adopted a resolution commemorating the victims of the concentration camp while calling to create a monument "in remembrance of thousands of Polish inhabitants of Warsaw who were murdered in the Warsaw concentration camp as part of the plan of annihilating the Capital City of Poland, as well as murdered citizens of other nationalities: Jews, Greeks, Gypsies, Belarusians and Italian officers".

[92] In March 2004, the Warsaw city council allowed to build a commemoration site on the Alojzy Pawelek square in the southern part of Wola district, next to what Trzcińska contended were gas chambers and subcamps of KL Warschau.

[134][135][i] That decision was opposed by supporters of Trzcińska's hypothesis, who argued that placing the monument there would suggest that only Jews were victims of the concentration camp, but the Supreme Administrative Court denied their request to invalidate the new resolution.