Action T4

In 1939, Oberhauser was assigned to Reichsarbeitsgemeinschaft für Heil- und Pflegeanstalten, part of the office for Action T4 and one of several front organizations of Hitler's Chancellery, in November 1939. This organization was responsible for the killing of approximately 100,000 mentally ill and disabled people during Action T4. At the killing centers of Grafeneck, Brandenburg and Bernburg, where these people were murdered en masse by gas (carbon monoxide poisoning), Oberhauser was a Brenner (burner), or Leichenbrenner (corpse burner): he was responsible for the burning of the bodies in the specially installed crematory ovens.

Operation Reinhard

Oberhauser (left), with Kurt Franz (right) and Jirmann (centre) at Belzec during Operation Reinhard

After finishing Action T4 in August 1941, in November Oberhauser was transferred to the staff of the SS and Police Leader (SSPF) for the Lublin district, SS-Brigadeführer Odilo Globocnik, to take part in Operation Reinhard, the extermination of Poland's three million Jews. From November 1941 until 1 August 1942, Oberhauser was posted to Bełżec extermination camp as the leader of a guard platoon. He first visited Bełżec in the fall of 1941, before the extermination camp existed, to remove military equipment at the site. He was responsible for the development of the camp. In December 1941, Oberhauser returned to Bełżec with construction materials and a team of Ukrainian Trawnikis. He was under the command of camp commandant Christian Wirth, and he also served as Wirth's liaison to Globocnik.^[3]

For his work in the implementation of Operation Reinhard, Oberhauser was promoted from SS-Hauptscharführer to SS-Untersturmführer, effective 20 April 1943, reaching officer rank in the SS. Previously, the Reichsführer-SS Heinrich Himmler had made a personal visit to the Operation Reinhard camps, including Bełżec, on 12 February 1943, and had decided to promote Oberhauser. In the 21 January 1965 judgment of the Munich District Court I (Case No. 110 Ks 3/64), his work at Belzec is described as follows (translated to English):

The defendant, Oberhauser, – then an SS-Oberscharführer – was on the staff of the senior SS and Police Leader in Lublin from November to Christmas 1941. Subsequently, he was assigned to work for the camp commandant of Belzec (Christian Wirth), which saw him appointed as liaison officer to the staff of the senior SS and Police Leader and moreover, unlike other non-commissioned officers, given no fixed area of responsibility within the camp; on the contrary, he was free to do as he personally saw fit. Consequently Oberhauser was often seen in Wirth's company within the camp, but no recognizable activity would have resulted nor would any independent authority have been exercised.

Only occasionally was Oberhauser given a role at the implementation of mass killings, the illegality of which he had fully recognized. For example, on the orders of the camp commandant, Wirth, he met trainloads arriving at Belzec, each comprising at least 150 people, at the camp gates on at least five occasions in the period from mid-March to 1st August 1942. He led the supervision of the unloading of the trains and made sure that the train crew did not enter the camp area but were held outside the camp in readiness, to be able to reinforce the outer cordon in case there was an uprising or desperate breakout attempt by the doomed people. All the Jews who arrived on these trains were killed in the manner already described.

When, in spring 1942, a major expansion of Belzec Camp was carried out to increase its capacity for extermination, it was the task of the defendant, to procure the necessary building materials, in particular, for the construction of the larger gas chamber facility. He was allocated vehicles and the people necessary for the fulfillment of this task. In exercising his duties, he was aware of the fact that the work carried out with his assistance, was intended to create the conditions for a significant increase in the numbers of those exterminated. On 1 August 1942, as inspector of the three extermination camps of Belzec, Treblinka and Sobibor, Wirth moved to his new office in Lublin, and succeeded in getting Oberhauser, whom he assessed as a dutiful subordinate, also transferred there. There, the defendant was given the command of the Ukrainian guards employed by the staff of the senior SS and Police Leader, Globocnik, to guard important sites in Lublin. In addition, he was still available to Wirth, and had to act as an escort on his inspection visits to the extermination camps.

— Belzec Trial - Sentence: LG Munich I dated 21 January 1965, 110 Ks 3/64. IV. The duties of the defendant in Belzec and Lublin.^[4]

Transfer to Italy

After the completion of Operation Reinhard, Oberhauser, along with many of his colleagues, was sent to northern Italy in the group Sonderabteilung Einsatz R to participate in anti-partisan warfare and the deportation and killing of Jews there. He was promoted to the rank of SS-Obersturmführer on 30 January 1945. Purportedly, Oberhauser was commandant of Risiera di San Sabba until its closure in late April 1945 (3,000 to 5,000 people died there). He then went to Austria with his unit, and was arrested by the British authorities in May 1945 in Bad Gastein.