Lefranc represented the interests of the "Commissariat Général aux Questions Juives" (CGQJ) as an"administrateur provisoire" of Jewish assets and also promoted the interests of Nazi officials in securing hidden Jewish collections. From 1942 to the end of 1943, Lefranc mobilized French and German resources to hunt down and seize the Schloss collection from which he profited.

He was prosecuted at war's end.