In 1939, Mandić was appointed a member of the central administration of the Franciscan Order in Rome as the representative of all the Franciscan provinces in Slavic countries, and Chief Economist of the Order. He was in Rome when war broke out in the Balkans in April 1941. As Chief Economist and General Definitor of the Franciscan Order, he provided financial support to the Ustasha, as Mark Aarons and John Loftus reference in Unholy Trinity: The Vatican, The Nazis, and The Swiss Banks. Mandić controlled San Girolamo ratline's finances. He arranged the laundering of Ustasha money likely via the Franciscans Vatican Bank accounts to which he had access and placed the Franciscan printing presses at the disposal of the Ustasha to print false identity information for war criminals to escape from justice after the Holocaust using ratline escapes. Other priests involved in the San Girolamo ratline included: Krunoslav Draganović, Dragutin Kamber, Vilim Cecelja (based in Austria) and Karlo Petranović (based in Genoa).