The Italian Minister of Defense, Giulio Andreotti, was responsible for the accident investigation. During his controversial tenure of ENI, Mattei had made many enemies. The U.S. National Security Council described him as an irritation and an obstacle in a classified report from 1958. The French could not forgive him for doing business with the pro-independence movement in Algeria. Responsibility for his death has been attributed to the CIA, to the French OAS, and to the Sicilian Mafia. According to a 2001 TV documentary by Bernhard Pletschinger and Claus Bredenbrock, evidence was immediately destroyed at the crash site. Flight instruments were put into acid. On 25 October 1995, the Italian public service broadcaster RAI reported the exhumation of the human remains of Mattei and Bertuzzi. Metal debris deformed by an explosion was found in the bones. There is speculation that the fuse of an explosive device was triggered by the mechanism of the landing gear. In 1994, the investigations were reopened. In 1997, a metal indicator and a ring were further analyzed by Donato Firrao of the Polytechnic University of Turin and explosion tracks were found. Based on this evidence, the episode was reclassified by the judge as homicide but with one or more perpetrators unknown. Not trusting the Armed Forces Information Service (Servizio informazioni forze armate, SIFAR), Italy's secret service, even though it was full of his loyal supporters, Mattei constituted a sort of personal security guard made of former partisans, ENI staff by whom he felt protected. Theories about his death According to , a former agent of the French secret service SDECE, SDECE agents were responsible for the 1962 plane crash which took the life of Mattei. Mattei was on the verge of engineering an Italian takeover of French oil interests in Algeria. A French agent code-named Laurent tinkered with Mattei's aircraft. When preparing the film The Mattei Affair in 1970, Francesco Rosi asked the journalist Mauro De Mauro to investigate the last days of Mattei in Sicily. De Mauro soon obtained an audio-tape of his last speech and spent days studying it. De Mauro disappeared eight days after his retrieval of the tape on 16 September 1970 without leaving a trace. His body was never found. All the Carabinieri and police investigators who searched for De Mauro, and consequently investigated his presumed kidnapping, were later killed. Among them the general Carlo Alberto Dalla Chiesa and Boris Giuliano