Conducted a worker's chorus under the pseudonym of Rosebery d'Arguto in a suburb of Berlin before the war. In 1939, he was arrested as a socialist and as a Jew and sent to Sachsenhausen, where he was brutally tortured. He later formed a chorus of 25 Jewish prisoners that carried out their activities in secret in the less guarded barracks for political prisoners. In 1942, when he discovered that the Jewish prisoners were to be sent to Auschwitz, he wrote the words to Tsen Brider (Ten Brothers), setting them to the melody of the old Yiddish folk song, "Yidl mit dem Fidl." Rosenberg and his chorus died in the gas chambers in 1943. This song was passed down by a non-Jewish prisoner at Sachsenhausen, Alexander Kulisiewicz, who survived the war. Rosenberg asked him not to forget Tsen Brider, and if he should survive, to sing the song and through it tell the world of the suffering in the death camps (from Leonarda Productions, Inc. website).