He also testified about the murder of journalist Mauro De Mauro. The investigative reporter had been kidnapped and killed by the Mafia in 1970. Di Carlo testified in 2001 that De Mauro was killed, because he had learned that one of his former fascist friends, Prince Junio Valerio Borghese, was planning a coup d'état (the so-called Golpe Borghese) with like-minded army officers determined to stop what they considered as Italy's drift to the left. Di Carlo became an important witness in numerous anti-mafia trials and also testified in the trials against former Prime Minister Giulio Andreotti and Silvio Berlusconi’s right hand man Marcello Dell'Utri.