He worked in the Sonderkommando for Crematorium 3. He lived in the attic of Crematorium 3 and observed the building and related activity. After his liberation he returned to Paris where he began to draw and record his memories. He produced over fifty sketches in 1945-46. Among the sketches Olere produced were architectural drawings of Crematorium 3 which show the basement level with the underground dressing room and the gas chamber, and the ground floor with the incineration room the ovens and the chimney.
Arrows indicate the functional relationship of the rooms.
In his drawings of Crematorium 3 and its environs Olere depicted people filing into the compound from the road and moving into the dressing room. A sketch from 1946 shows the dressing room, the benches and the hooks for clothes. Another sketch shows the Sonderkommandos collecting gold teeth and hair from the women. One of the wire mesh columns is visible in the background. He also pointed out that none of the drawings could have been made on the basis of published material as there was not any available at the time.