Marcel Grüner
Marcel Grüner was an inhabitant of the Krakow ghetto. He was a handsome man, a trader, selling and buying various goods, including cosmetics. Arrested by Gestapo
(german: Geheime Staatspolizei) The Secret State Police established in the Third Reich, which ruthlessly fought against all forms of resistance in the occupied territories. Identified with the most terrible German crimes against Poles, and after 1942 also against Jews. Disbanded with the fall of the Third Reich in 1945. Recognized as a criminal organization by the International Military Tribunal in Nuremberg., he was released after three days. He agreed to become a secret informant for the customs and tax office due to his knowledge of trade and finance.
Grüner dealt with finding hiding Jews and denouncing them to the Gestapo. It was his doing that many of his brothers-in-faith died in extermination camps. But his work was not limited to only denouncing people in hiding. He was also involved in the investigation of the [Jewish Fighting Organization] fighting against Jewish informers and the Germans. He was tracking its members and reported to the Gestapo. Apparently, he boasted that he would be able to go abroad. Perhaps this raised suspicions that he was working as a Nazi collaborator.
He often visited The Eagle Pharmacy, which was run by Tadeusz PankiewiczTadeusz Pankiewicz (1908 - 1993) - Polish pharmacist, graduate of the Jagiellonian University, owner of the "Pod Orłem" (polish: "Under the Eagle") pharmacy in Krakow, the only pharmacy operating in the Krakow ghetto. He came from a family with patriotic traditions. For his activity in aiding and rescuing Jews, he was awarded the medal "Righteous Among the Nations". He described his wartime memories in a book entitled "Apteka w getcie krakowskim" ("The Cracow Ghetto Pharmacy").. This is where the Jewish elite met. Fortunately, he never managed to throw in a Polish hero who was saving Jews. Suspected of working for the Gestapo, he was deliberately made drunk with alcohol during one of the meetings. His coat was searched. Documents were discovered that allowed him to move freely around the ghetto and to leave it anytime. This made it clear that Grüner was a Gestapo informer.
It is known that an attempt was made to liquidate the informer. Grüner survived, but one of the underground men, Robert Offner, died.
Witold MędykowskiPrzeciw swoim. Wzorce kolaboracji żydowskiej w Krakowie i okolicy
https://wiadomosci.onet.pl/tylko-w-onecie/tadeusz-pankiewicz-zapomniany-bohater/c6nnd2