Originally a supporter of Benito Mussolini's Fascist regime, De Mauro eventually became a journalist with the left-leaning newspaper L'Ora in Palermo.

His father Oscar De Mauro belonged to a reputable family of doctors and pharmacists that had been living in Foggia for several generations.

[5][6] Using a variety of aliases, De Mauro managed to infiltrate several resistance organizations in Rome and Milan in order to hunt the partisans.

He escaped from the prison camp Coltano (Tuscany) in December 1945 and took refuge in Naples with his young wife, along with his two daughters, Junia and Franca Valeria (the names referred to Junio Valerio Borghese).

Other journalists were puzzled about De Mauro's presence at the newspaper, as he had been a supporter of Mussolini until the bitter end and fought in the brutal war against the anti-Fascist partisans.

[1] At L'Ora, De Mauro joined a group of crack investigative reporters that included Felice Chilanti and Mario Farinella.

From the mid-1950s to the 1970s, the left-leaning newspaper often hit the national spotlight for its investigations and denunciations of ties between corrupt politicians and the Sicilian Mafia.

[15] and in 1959, in the middle of the Cold War, brokered an oil import deal with the Soviet Union over intense protests from the United States and NATO, while supporting independence movements against colonial powers such as Algeria.

[1][2] De Mauro was kidnapped on the evening of 16 September 1970, while coming back home from work, in the via delle Magnolie in Palermo.

"[2] According to Giuliano, an order to scale down the investigation was issued by the head of the secret service, Vito Miceli, allegedly involved in the Borghese coup.

[27] According to Buscetta, Mattei was killed at the request of the American Mafia because his oil policies had hurt U.S. interests in the Middle East.

[28][29] Gaetano Iannì, another pentito, declared that a special agreement had been reached between the Sicilian Mafia and "some foreigners" for the elimination of Mattei, which was organized by Di Cristina.

[28][29] Another pentito, Francesco Di Carlo, declared in 2001 that De Mauro was killed because he had learned that one of his former fascist friends, Prince Borghese, was involved in the planned 1970 coup with like-minded army officers, determined to stop what they considered as Italy's drift to the left.

[1][2][31] Yet another pentito, Rosario Naimo, who started to collaborate with the Italian authorities after his arrest in October 2010, said that the journalist was killed because of his investigative reporting that damaged the Mafia.

[32] The order for De Mauro's killing came from the heads of the Sicilian Mafia Commission, Bontade, Gaetano Badalamenti and Salvatore Riina, according to Di Carlo and Buscetta.

[33] According to the new testimony of Naimo, De Mauro was taken to a terrain in Pallavicino neighbourhood in Palermo where the Mafia boss Francesco Madonia owned a chicken farm.

[37] The "inconvenient journalist" (giornalista scomodo), as De Mauro had become known, was kidnapped and killed because the Mafia and their backers wanted to know his sources of confidential and potentially devastating information, public prosecutor Antonio Ingroia told the court in his closing speech in March 2011.

Riina, Bontade, and Badalamenti decided to eliminate De Mauro because he was about to go public about Mattei's 1962 murder as a result of research for Francesco Rosi's landmark movie, as well as the fact the journalist had uncovered the plans for staging the Mafia-backed far-right Borghese coup d'état, thanks to his former wartime Fascist connections.

The other 'convergent' element in his death was the fact that he knew, from its inception, about the subversive project involving spies, neofascists and Mafia groups [to stage the Borghese Coup].

From his sources in neofascist circles, from his past in Prince Junio Valerio Borghese's crack Decima Mas unit, as well as from tip-offs from Mafia boss Emanuele D'Agostino, he knew something was in the offing.

[39] Cosa Nostra was behind the murder of De Mauro, but there were other backgrounds and individuals, allied with the Mafia, such as deviated freemasons and corrupt public officials.

The Court concluded that De Mauro most likely had been killed by the Mafia because he knew of their involvement in Enrico Mattei's death rather than the Borghese coup attempt.