The investigations led by the Italian authorities soon after the war were ineffective, superficial and encumbered by various bureaucratic obstacles. Captain Carlo Galli of the police was responsible for the investigation. He didn't know anything about the American or British investigations because nobody more senior in the responsible institutions had informed him about them.
The 3 superficial reports that Captain Galli sent to the Prefect of Bologna and then to the General Attorney of the Supreme Military Court in Rome from June 1946 to May 1947 were full of irrelevant and vague documents, some of which were not connected to the events at Monte Sole.
Even in May 1947 Galli was not sure of the name of the SS Division responsible for the massacre at Monte Sole. This is particularly strange when one considers that he physically met the British Lieutenant Jones who was carrying out an investigation at the same time on the same events, and obtaining far more useful evidence. Also the few relevant documents collected by Galli got lost in the corridors of bureaucracy.
These circumstances did not even change after the intervention on 22nd February 1947 by the mayor of Marzabotto who asked Allied Headquarters in Italy that testimony from the townhall be submitted in the trial against Field Marshal Albert Kesselring (which started at that time). The Allies passed on the decision to the Italian Ministry of the Interior where nothing happened either because it was buried in bureaucracy or there was a real lack of political will.
Source: From Pezzino and Baldissara, Il massacro. Guerra ai civili a Monte Sole, Bologna, Il Mulino, 2009, p. 388-395.