Thursday Book: The darkness at the heart of Italy's legal system

The Judge and the Historian: marginal notes on a late 20th-century miscarriage of justice by Carlo Ginzburg, translated by Anthony Shugaar (Verso, pounds 17)

THE YEAR 1969 was a productive one for the Italian left. In Turin, where students campaigned alongside Fiat workers, a dispute about the nature of class struggle spawned two national movements: Potere Operaio (Workers' Power) and Lotta Continua (Continuous Struggle). In Milan, a smaller group came together, the Metropolitan Political Collective. That December, a bomb in the Banca dell'Agricoltura in Milan killed 16 people.

The bombing was widely denounced as a "state massacre" - a judgement later endorsed by historians of the "strategy of tension". The members of the Metropolitan Political Collective reacted by committing themselves to "armed struggle" and taking a new name: the Red Brigades.

Police investigations focused on the anarchist scene. On the night of 15 December, the anarchist Pino Pinelli fell to his death from a window at Milan's police headquarters. Lotta Continua maintained that Pinelli was already dead when he fell, killed by Luigi Calabresi, the officer in charge of the investigation. In 1972, Calabresi was shot dead outside his house. While not endorsing the murder, Lotta Continua described it as "a deed in which the exploited recognise their own yearning for justice".

Lotta Continua was a heterodox, libertarian group, but in 1976 the group's own pluralism tore it apart. The leaders, including the charismatic Adriano Sofri, embraced electoral politics; many militants embarked on the quixotic project of libertarian terrorism.

Out of the blue, 12 years later, Sofri and two other former Lotta Continua militants were arrested. Sofri was charged with ordering the murder of Calabresi. His accuser was a former Lotta Continua member, Leonardo Marino, who claimed that he had driven the getaway car, a beige Fiat, past the site of the shooting, and reversed for 10 metres. He then had "bushy" hair and "a very visible moustache". In fact, the car was blue; several eyewitnesses agree that it stopped opposite Calabresi's house, and that the driver was a long-haired woman.

These unlikely stories - among others - have been taken for fact by the highest courts in Italy. The only part of Marino's testimony that has been corroborated - his membership of Lotta Continua - has somehow served to underwrite all his other claims and to incriminate the group.

In 1990, Sofri and his co-defendants were sentenced to 22 years in prison. The sentences, repeatedly struck down and reinstated, were put into effect in 1997. Giorgio Pietrostefani, one of Sofri's co-defendants, returned to Italy from France to serve - and contest - his sentence.

The great historian Carlo Ginzburg first wrote about the Sofri case in 1991; this new edition includes recent appeal-court judgments. Ginzburg seems to have set out to examine the differences between legal and historical standards of proof, using the case as a reference point. In practice, the material takes a different form. Unhelpful eyewitness accounts are demolished by hostile police questioning. Or witnesses who back Sofri can be discounted, simply because they back Sofri. Many moments evoke nothing so much as Ginzburg's previous work on witch trials.

There are some parallels with the case of Toni Negri, the leader of Potere Operaio, who was arrested in 1979 and charged with co-ordinating the actions of Potere Operaio and the Red Brigades. The prosecutor, Pietro Calogero, argued that the two organisations were complementary. The "Calogero Theorem" was supported only by passages in Red Brigades documents that seemed to echo Negri's writings. Calogero argued that this was adequate, as hard evidence would inevitably be unavailable. This reasoning sufficed to earn Negri a 30-year prison sentence, passed in absentia. He went into exile in 1983.

Negri returned to Italy in 1997 and is now fighting his sentence from inside prison. But even after verdicts whose delirious argumentation makes the Calogero Theorem look almost rational, Sofri and his supporters retain some respect for the legal system. Sofri's son Luca stresses the implications of the verdict for Italy's future. If the system cannot rectify the injustice, a dangerous precedent will have been set. Ginzburg concludes: "This shameful page in the history of Italian justice must be erased - and as soon as possible."