He served as an SS NCO in three extermination camps during World War II in German occupied Poland and Germany: Auschwitz, Majdanek and Flossenbürg.

[2] However, Muhsfeldt was then extradited to Poland, where the full extent of his war crimes was revealed due to new evidence.

He was retried by the Supreme National Tribunal at the Auschwitz Trial in Kraków, and found guilty of crimes against humanity.

According to Miklós Nyiszli,[5] his wife was killed in an air raid, and his son sent to the Russian front.

He was present at the final mass shooting of the camp's remaining Jewish inmates known as the Operation Harvest Festival or "Erntefest, the largest single-day, single-camp massacre of the Holocaust,[6] totalling 43,000 in three nearby locations.

[7] Muhsfeldt testified of the incident before the Polish Court in Kraków in 1947: One day in late October 1943 the excavation of pits was begun behind Compounds V and VI, approximately 50 meters behind the structure of the new Crematorium.

Then Commander Anton Thumann cut the wires of the fence separating Compound V from those pits, making a passageway.

According to testimony at the Majdanek trials at one "selection" at KZ Majdanek a female KZ inmate scratched Muhsfeldt face asking why she had to die; Muhsfeldt ordered her to be bound and thrown alive into a Crematorium[8] When the Majdanek camp was liquidated, Muhsfeldt was transferred back to Auschwitz, where he then served as supervising SS officer of the Jewish Sonderkommando in Crematorium II and III in Auschwitz II (Birkenau).

[9] Upon his return to Auschwitz, Muhsfeldt had an unusual relationship with renowned Jewish-Hungarian pathologist Miklós Nyiszli, who was forced to carry out autopsies on behalf of Josef Mengele.

According to Nyiszli, "[Muhsfeldt] often came to see me in the dissecting room, and we conversed on politics, the military situation and various other subjects.

Nyiszli described one incident when Muhsfeldt came to him for a routine check-up, after shooting 80 prisoners in the back of the head prior to their cremation: Later Mussfeld(sic) paid me a visit and asked me to give him a physical check up.

Nyiszli explains that "Half an hour later the young girl was led, or rather carried, into the furnace room hallway, and there [Muhsfeldt] sent another in his place to do the job.

A bullet in the back of the neck..."[10] After the war had ended, Muhsfeldt was arrested by U.S. military officials.

However, he was then extradited to Poland where he was retried in Kraków by the Supreme National Tribunal in November 1947 for crimes committed in Auschwitz.

[11] Muhsfeldt appears as a minor character in the 1983 James Michener novel Poland, and is portrayed by Harvey Keitel in the 2001 film The Grey Zone.