
A large percentage of those who were killed at Auschwitz-Birkenau,
were not cremated in the 46 crematory muffles there (15 each in
Krema II & III, 8 each in Krema IV & V), many were cremated in pits.

All the victims of Bunkers I & II, the original gas chambers at Auschwitz-Birkenau
were cremated in pits, and victims from the gas chambers in Krema IV & V were
often cremated in pits, as documented in the famous fake photo above.
Witnesses at the 1947 trial of former Auschwitz commandant Rudolph Hoess (centre), claimed
that in one night alone, 40,000 people were burnt alive in an immense pit at Birkenau.
Claude Lanzmann's 9 hour long film/documentary Shoah includes an interview with Filip Müller, a Czech Jew who spent 3 years gassing and burning Jews at Auschwitz, and once ate cheese which he found in the gas chamber.

Filip Müller describes an incident when the crematory ovens in the same building as the very first
Auschwitz gas chamber in Auschwitz I were out of action, and approximately 300 corpses, who
had been killed in the gas chamber, were loaded onto trucks and taken to a field in Birkenau.
Filip Müller states:
"We were ordered to unload the bodies and put them in a pit. There was a ditch, an artificial
pit. Suddenly, water gushed up from underground. And swept the bodies down."
"The next day we were taken to the same place but the water had risen. Some SS men cam with a
firetruck and pumped out the water. We had to go down into that muddy pit to stack up the bodies.
But they were slimy. For example, I grasped a woman by her hands ... Her hand was slippery, slimy.
I tried to pull her, but I fell over backwards into the water, the mud. It was the same for all of us."
Jean Claude Pressac in Auschwitz: Technique & Operation of theGas Chambers states of the high water table at Auschwitz-Birkenau:
"The nature of the land at Birkenau, where the groundwater is almost at surface
level (unlike the main camp, where it lies deeper), meant that the two Leichenkeller
[“corpse cellars”] could no longer be directly under the building, as had probably
been initially planned, but had to be raised to form semi-basements."
Szlamy Dragon former Auschwitz sonderkommando claimed he helped burn Jews in:
"four pits 30 meters long, 7 meters wide and 3 meters deep"
Miklós Nyiszli a Jewish doctor at Auschwitz states:
"The pyre was a ditch 50 yards long, six yards wide and three yards deep."