Shrinking support for the Christian Democrats eventually led to the Socialist party gaining power in the sixties, with the Christian Democrats being forced to accept a coalition. The attempt to bring in the neo-fascist Italian Social Movement (MSI) in the Tambroni government led to riots, and were short-lived. A left-wing autonomist movement, in the wake of student unrest ("Sessantotto"), lasted from 1968 until the end of the Seventies.
This period became known as the anni di piombo ("years of lead", i.e., [bullets]) from a wave of bombings and shootings — starting with the 1969 Piazza Fontana bombing by neofascists — attributed to the far-right, far-left and secret services. According to the Ministry of Interior, 67.5% of the violence ("brawls, guerrilla actions, destruction of goods") committed in Italy from 1969 to 1980 are attributable to the far right, 26.5% to the far left, and 5.95% to others. 150 people were killed in terrorist actions carried out by the far right, and 94 by the far left .
Social protests, in which the autonomist student movement was particularly active, shook Italy during the 1969 autunno caldo (Hot Autumn), leading to the occupation of the Fiat factory in Milan. Mario Capanna, associated with the New Left, was one of the many important figures of that movement, along with the members of Potere Operaio and Autonomia Operaia (Antonio Negri, Oreste Scalzone, Franco Piperno, etc.), Lotta Continua (Adriano Sofri, etc.), etc.
The police immediately arrested 4,000 people in left-wing circles, including Giuseppe Pinelli, an anarchist who was initially blamed for the bombing, and Pietro Valpreda. This was hotly denied by left-wingers, especially the student movement, at the time very strong in Milan's universities, who believed the bombing was committed by fascists. The newspaper of Lotta Continua accused the state security services of being behind the bombing. Following the "accidental death" of Giuseppe Pinelli who "fell out of a window" on 15 December 1969 while in police custody (see Dario Fo's Accidental Death of an Anarchist, first presented in 1970), the radical left-wing newspaper initiated a campaign accusing police officer Luigi Calabresi of having murdered Pinelli. Meanwhile, the anarchist Valpareda was sentenced to prison for the bombing. After 16 years, he was released, the Italian state recognizing a miscarriage of justice.
The accusation of Lotta Continua proved to be correct, but only after many years of difficult investigation. The neofascist Vincenzo Vinciguerra was finally arrested in the 1980s for the bombing, and confessed to magistrate Felice Casson that this false flag attack had been intended to force the Italian state to declare a state of emergency and become authoritarian. Vinciguerra explained how the SISMI military intelligence agency had protected him, allowing him to escape to Spain. Neo-fascist terrorists from Ordine Nuovo were accused of the crime, along with a US naval officer suspected of involvement .
Violent demonstrations took place in Pisa on May 5, 1972, when young people, summoned by Lotta Continua, tried to prevent a meeting of the neofascist MSI. During the confrontations, a young anarchist, Franco Serantini, was brutally hit by police batons, and died two days later in prison, denied care. On May 17, 1972, police officer Luigi Calabresi was assassinated in Milan. Authorities first pointed to people in Lotta Continua, before indicting two neofascist activists, Gianni Nardi and Bruno Stefano, along with the German Gudrun Kiess in 1974. They were eventually released. Sixteen years later, Adriano Sofri, Giorgio Petrostefani and Ovidio Bompressi were arrested in Milan, on the grounds of a confession from a pentito. Highly controversial, the trial finally concluded with their guilt. Historian Carlo Ginzburg wrote The Judge and the Historian. Marginal Notes and a Late-Twentieth-century Miscarriage of Justice, which criticized the lack of evidence and the dependence solely on the controversial pentito. In any case, Calabresi's death was the first political assassination of the 1970s.
Two weeks later, a bombing in Peteano killed three carabinieri. This was blamed on Lotta Continua by carabinieri officers, some of whom were convicted of hampering the investigations Years later, the neofascist Vincenzo Vinciguerra confessed to having carried out the Peteano attack. Magistrate Felice Casson found out in the 1980s that the bomb was made from military C-4 explosive from a Gladio (Cold War NATO stay-behind anticommunist network) dump near Verona.
"Casson's investigation revealed that the right-wing organization Ordine Nuovo had collaborated very closely with the Italian Military Secret Service, SID (Servizio Informazioni Difesa). Together, they had engineered the Peteano terror and then wrongly blamed the militant extreme Italian left, the Red Brigades. Judge Casson identified Ordine Nuovo member Vincenzo Vinciguerra as the man who had planted the Peteano bomb... He confessed and testified that he had been covered by an entire network of sympathizers in Italy and abroad who had ensured that after the attack he could escape. 'A whole mechanism came into action', Vinciguerra recalled, 'that is, the Carabinieri, the Minister of the Interior, the customs services and the military and civilian intelligence services accepted the ideological reasoning behind the attack.'"
Despite these provocations, Interior Minister Mariano Rumor refused to proclaim a state of emergency. During a ceremony honouring Luigi Calabresi, in which the Interior Minister was present, on 17 May 1973, an alleged anarchist, Gianfranco Bertoli, threw a bomb killing four and injuring 45. In 1990, it was discovered that Bertoli, who had been convicted for the bombing, was an SID informant and member of Gladio. The secret services claimed it was only a coincidence, although, a short time before his death, Luigi Calabresi had opened up a file on Bertoli. A magistrate investigating the assassination attempt of Mariano Rumor found that Bertoli's files were incomplete .
General Gianadelio Maletti, head of the SID from 1971 to 1975, was convicted in absentia in 1990 for obstruction of justice in the Mariano Rumor case. The investigation revealed that he had known of the attack before-hand, but had deliberately failed to prevent it. Testifying in 2001 on the 1969 Piazza Fontana bombing (with a special immunity), General Maletti declared:
""The CIA, following the directives of its government, wanted to create an Italian nationalism capable of halting what it saw as a slide to the left and, for this purpose, it may have made use of rightwing terrorism... I believe this is what happened in other countries as well...Don't forget that Nixon was in charge and Nixon was a strange man, a very intelligent politician but a man of rather unorthodox initiatives"
Maletti further declared that:
"Among the larger western European countries, Italy has been dealt with as a sort of protectorate. I am ashamed to think that we are still subject to special supervision."
Count Edgardo Sogno revealed in his memoirs that in July 1974, he visited the CIA station chief in Rome to inform him of preparations for a neo-fascist coup. Asking what the US government would do in case of such a coup, Sogno wrote that he was told, "the United States would have supported any initiative tending to keep the communists out of government." General Maletti declared, in 2001, that he had not known about Sogno's relationship with the CIA and had not been informed abouit the coup, known as Golpe bianco (White Coup), led by Randolfo Pacciardi .
General Vito Miceli, chief of the SIOS military intelligence agency from 1969, and head of the SID from 1970 to 1974, was arrested in 1974 on charges of "conspiracy against the state." Following his arrest, the Italian secret services were reorganized by a 24 October 1977 law in an attempt to regaining civilian and parliamentary control. The SID was divided into the current SISMI, the SISDE and the CESIS, which was to coordinate and was directly led by the Prime Minister of Italy. Furthermore, an Italian Parliamentary Committee on Secret services control (Copaco) was created at the same time.
In 1974, the leaders of the Red Brigades including Renato Curcio and Alberto Franceschini, were arrested. The year before, Potere Operaio had disbanded, although Autonomia Operaia carried on some of its plans. Lotta Continua also dissolved in 1976, although the magazine struggled on for several years.
One of the last and largest of the bombings, known as the Bologna massacre, destroyed the city's railway station in 1980. This was a fascist bombing, mainly organized by the Nuclei Armati Rivoluzionari (NAR), who had ties with the Roman criminal organization Banda della Magliana. Four years later, on December 23, 1984, another bombing in a train between Florence and Rome killed 16 and wounded more than 200. The mafiosi Giuseppe Calò and four other defendants were sentenced to life imprisonment in 1989 for the latter. According to the prosecutors, the far-right had conspired with the mafia and the Camorra to carry out this attack .
Many aspects of the "years of lead" are still shrouded in mystery, and debate is still going in regard to some of it. There are many, especially among the left, who speak of the existence of a strategia della tensione. According to this theory, secret and foreign forces were involved, among whom Gladio, a NATO secret anti-communist structure, the Propaganda Due masonic lodge]], revealed in 1981 after the arrest of its leader Licio Gelli, and fascist "black terrorism" organizations such as Ordine Nuovo or Avanguardia Nazionale, Italian secret services as well as the United States. The existence of Propaganda Due (aka P2) was discovered in 1981, during the Banco Ambrosiano scandal and the 1982 assassination of Roberto Calvi, nicknamed "God's Banker" as the Vatican Bank, presided by Paul Marcinkus, was the main share-holder of Banco Ambrosiano. In 1981, the police found in Licio Gelli's villa on the Côte d'Azur in France the list of more than 900 members of P2, including 30 generals, 38 members of parliament, four cabinet ministers, former prime ministers, intelligence chiefs, newspaper editors, TV executives, businessmen, bankers, 19 judges, and 58 university professors. Among them: Silvio Berlusconi, General Vito Miceli, Michele Sindona and Roberto Calvi, Maurizio Costanzo, Fabrizio Cicchitto and investigative journalist Carmine Pecorelli.
This theory reemerged in the 1990s, following Prime minister Giulio Andreotti's recognition of the existence of Gladio before the Parliamentary assembly on 24 October 1990. Furthermore, juridical investigations concerning the Piazza Fontana bombing and the Bologna massarce, in particular by Milan prosecutor Guido Salvini — who indicted a US Navy officer, David Carrett, for his role in the Piazza Fontana bombing, and surprised in 1995 Carlo Rocchi, CIA's man in Italy, searching for information concerning the case in the mid-1990s — and several parliamentary reports pointed towards such a deliberate strategy of tension.
In 2000, a Parliament Commission report from the Olive Tree left-of-center coalition concluded that the strategy of tension had been supported by the United States to "stop the PCI, and to a certain degree also the PSI, from reaching executive power in the country".