Responsible for investigating far-left political movements, Calabresi was assassinated in 1972 by members of Lotta Continua, who blamed him for the death of anarchist activist Giuseppe Pinelli in police custody in 1969.

[7][8][N 1] Mario Capanna of the Marxist group Movimento Studentesco joined the funeral procession in a public gesture of denunciation of political violence, but was physically attacked by a number of attendees.

On 12 December 1969, at 16:37 hours local time,[N 2] a bomb exploded at the headquarters of Banca Nazionale dell'Agricoltura (the National Agricultural Bank) in Piazza Fontana, near the Duomo cathedral, in Milan, Italy, killing seventeen people and wounding eighty-eight.

[2] Directed by his superiors in Rome to investigate the anarchists that were part of the so-called Ghisolfa Bridge group, Calabresi ordered the round up of approximately eighty suspects.

[9] In commissioner Calabresi's office were present Antonio Allegra and four policemen from the political section, Vito Panessa, Giuseppe Caracuta, Carlo Mainardi, and Pietro Mucilli, as well as Carabinieri lieutenant Savino Lograno, subsequently identified as a SISDE agent.

The autopsy ostensibly showed that Pinelli had been "either dead or unconscious" as he hit the ground, with a bruise like one, Fiorenzano claimed, caused by a kick, "possibly a karate blow," found on his neck.

On the 16 December 1969, the day after Pinelli's death, Milan chief of police Marcello Guida called a press conference that was also attended by Antonino Allegra and commissioner Calabresi.

I can say that we did not regard him as some key witness, but merely as someone to be heard.”[19] On 27 December 1969, Pinelli's widow Licia and his mother sued and filed a complaint against Milan police chief Marcello Guida in relation to actions that, as they asserted, constituted "ongoing and aggravated defamation" as well as "breaches of professional confidentiality and conduct".

It was remarked that the "advanced state of [the body's] decomposition" had rendered the second autopsy futile[19] but also that the "bruising" that some considered suspect was a frequent consequence in corpses housed in morgues because of the compression of the head on the marble table.

[20] In 1975, D'Ambrosio closed the investigation by establishing that Calabresi had not been present in the room at the time of Pinelli's fall and that the "suicide thesis" was unlikely due to lack of any plausible motivation.

D'Ambrosio considered instead as most probable a death causata da un malore, "caused by an active illness," thus ruling out defenestration homicide; consequently, all those accused or present in the room were exonerated.

The Socialist Party's newspaper Avanti!, the PCI's daily l’Unità and its weekly companion Vie Nuove took up a campaign of denunciation against Italian law enforcement and Calabresi specifically.

[19][28] On 15 April 1970, Calabresi brought charges against Pio Baldelli, editor-in-chief of the Lotta Continua magazine, for "ongoing and aggravated defamation through attribution of a specific act", to wit, the responsibility for Pinelli's death.

The previous month, in September 1970, L’Espresso weekly magazine had carried the public appeal made and signed by various Italian intellectuals, university lecturers, and politicians, such as Elvio Fachinelli, Lucio Gambi, Giulio Maccacaro, Cesare Musatti, Enzo Paci, Carlo Salinari and Mario Spinelli.

Their open letter issued a challenge: “Railway man Pino Pinelli died on the night of 15–16 December 1969 as a result of a fall from a window at Milan police headquarters.

Brigadiere Vito Panessa ended his testimony at the trial with the following statement: I've said I'm not in a position to provide details but, broadly speaking, bear in mind that there was no agreed story and it was, therefore, a matter for investigation.

In early 1974, neofascist journalist and SID operative Guido Giannettini told a reporter from L'Espresso that the Bundesnachrichtendienst or BND had "arranged" for Calabresi's assassination when they learned that the commissioner discovered that the West German intelligence service was furnishing "concrete" assistance to certain extreme-right groups in Italy, possibly to be used in terrorist acts or even a coup d'état.

In mid-1974, right-wing militant Marcello Bergamaschi testified to the Italian police that Carlo Fumagalli, his chief in the armed, far-right group Movimento di Azione Rivoluzionaria, "knew many things" about the assassination.

In 1979, a document was discovered at a safe house of the armed, extreme-left group Prima Linea that termed Calabresi's death "an act of proletarian justice," a finding that re-activated the investigation towards the extreme left.

"[33]: 389  Marino detailed how, on 13 May 1972, four days before the attack on Calabresi, he'd met Sofri in Pisa, during a gathering organized by Lotta in commemoration of the death of the anarchist Franco Serantini.

[34] On 2 May 1990, Adriano Sofri, Ovidio Bompressi and Giorgio Pietrostefani were each found guilty of Calabresi's murder and sentenced by the Milan criminal court to 22 years in prison.

[36] The historian Paul Ginsborg casts doubt on the final verdict, noting the sixteen-year gap between the crime and Marino's confession and the lack of other corroborating evidence.

[34] In November 2005, Sofri, who had refused offers of political supporters to appeal for a pardon, suffered a ruptured oesophagus and, after convalescing in a hospital, the court allowed him to serve the remainder of his sentence under house arrest, at his Impruneta home.

On 17 May 2022, coincidentally fifty years exactly after Calabresi's assassination, the Paris Court of Appeal heard the public prosecutor's proposal for Pietrostefani to be extradited to Italy to serve his prison sentence and decided to postpone its decision until the 29th of June.

At the conclusion of the Congress, Adriano Sofri gave a summing up speech in which he "pointed the finger" at the leadership for being "irresponsible in the face of [internal] contradictions," and asserted the existence of "an ambiguity that has accompanied the entire life of the organization."

[49][N 7] Film director Folco Quilici and photographer Oliviero Toscani denied having affixed their signature to the document, in the first place, while Giampaolo Pansa explained in an editorial why he'd refused to sign it when it was presented to him.

On 14 May 2004, Carlo Azeglio Ciampi, President of the Italian Republic, presented Gemma Capra with the Medaglia d'Oro al Valor Civile in memoriam of Luigi Calabresi as a victim of terrorism.

[20] In 2017, Cardinals Angelo Scola and Gaetano Vallini, respectively archbishops emeritus of Rome and Milan, commenced a new campaign to gather support for the beatification of Calabresi, whose death, they asserted, was in odium fidei, "in hatred of the faith.

"[53] The story of the Piazza Fontana massacre and the deaths of Pinelli and Calabresi were the inspiration for Marco Tullio Giordana's 2012 film Romanzo di una strage (Novel of a massacre; released outside Italy as Piazza Fontana: The Italian Conspiracy), in which Calabresi was portrayed by Valerio Mastandrea, and also of the 2014 television miniseries Gli anni spezzati - Il commissario (The broken years - The commissioner), with Emilio Solfrizzi as protagonist.

In the evening event, the family members spoke of the past, with Gemma declaring that she holds no hatred for the culprits, having decided "a long time ago" to "make peace with life."