In the West he was for decades one of the world's most wanted leftist terrorists, but in communist East Berlin, Carlos the Jackal was given a headquarters with 75 support staff and allowed to walk the streets with an automatic pistol slung from his belt.

The extraordinary life of Illich Ramirez Sanchez – the internationally renowned terrorist now serving a life sentence in Paris for triple murder – behind the Iron Curtain began to emerge yesterday from a mass of torn East German Stasi files that are slowly being put back together by the German authorities.

Sanchez, who was nicknamed "Carlos the Jackal" when it became known that police once found a copy of Frederick Forsyth's novel The Day of the Jackal among his belongings, is reported to be responsible for the deaths of at least 80 people during a terrorist career spanning 25 years. Carlos, an acclaimed film about his life, went on general release this week.

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For decades he worked as a hit man for the left-wing Popular Front for the Liberation of Palestine (PFLP) leading a murderous if spectacular raid on the Organisation of the Petroleum Exporting Countries' Vienna headquarters in 1975. Sixty hostages were taken and three people were shot dead.

But a year later the Venezuelan-born Sanchez, who was given his first name Illich by his Leninist lawyer father, found himself expelled from the PFLP and tyring to form his own guerrilla group, the Organisation of Armed Struggle. It was then that Sanchez turned to East Germany. As the Stasi's reconstituted secret police files revealed yesterday, the hardline communist regime afforded Carlos hitherto unimagined levels of assistance.

According to Germany's Focus magazine, which gained access to the files, Sanchez formed a pact with East Germany in the late 1970s. The communist authorities allowed him to run a headquarters in East Berlin which was staffed by 75 helpers hand-picked by the Stasi.

"While the West's security forces were feverishly trying to track down and arrest him, Sanchez remained completely at ease in East Berlin," said one of the Focus journalists. "His Stasi minders wrote reports about how he used to ride around in West German cars with his friends and walk across the city's main square with a pistol attached to his belt," he added.

Sanchez's support staff included East German university lecturers, actors, trade union functionaries, nurses, mechanics and even a doctor. They helped furnish him with safe houses, apartments for conspiratorial meetings, "secure" telephone lines and ensured that his car, always a West German model, was kept in perfect running order.

The Stasi helped not only Sanchez, but also arranged doctors' appointments for his then girlfriend, Magdalena Kopp, and her colleague, the West German terrorist Johannes Weinrich.

East Germany's support for Sanchez was apparently far greater than the assistance given by the regime to West Germany's Red Army Faction. The terrorist group carried out a string of bombing, kidnappings and murders in 1970s and 80s. Its members were given safe houses in East Germany when they were on the run from the West German authorities. East Germany also had close links with Palestinian groups and Libya.

From East Berlin, Sanchez is believed to have planned attacks on Radio Free Europe's office in Munich and a 1983 attack on West Berlin's Maison de France, a French cultural centre, which killed one man and injured 22 others. Bomb attacks on two French TGV trains which killed four and injured dozens followed in the same year. According to the files, Sanchez's close links with the Stasi enabled the secret police to put pressure on him to refrain from carrying out terrorist attacks at sensitive moments. When the former Soviet leader Leonid Brezhnev visited West Germany in November 1981, the files show that the KGB submitted a request to the Stasi to intervene to "prevent any activities" by Sanchez during the visit. The request apparently worked, because, although western intelligence was aware that the group was planning an imminent West German attack, the visit passed off without incident.

The revelations about Sanchez have emerged from some 15,500 rubbish sacks stuffed with torn or shredded secret police files that Stasi officers frantically tried to destroy in the aftermath of the fall of the Berlin Wall in 1989. The sacks were meant to be taken to rubbish dumps and burned, but protesters occupied East Berlin's Stasi headquarters and prevented their removal.

However it was not until 1995 that reunited Germany began attempting to reconstitute the damaged files using archivists to do the painstaking work by hand. Two years ago staff at the government office which oversees the files reported that they had managed to put together 900,000 Stasi file pages from 400 of the sacks. The contents have helped further to expose the iniquities of a secret police system in a state in which around every fourth citizen was an informer. A computer is now being used in a pilot study designed to rebuild the files electronically.

French and US intelligence eventually persuaded the authorities in Sudan, where Sanchez eventually lived, to arrest him. He was captured and tranquilised by his own bodyguards after undergoing a minor operation on a testicle in 1994. He was then handed to French intelligence agents and flown to Paris to stand trial.

In 1997 he was sentenced to life imprisonment after being convicted of the 1975 murder of two French policemen and a former PFLP guerrilla-turned-informant. Sanchez, who married his trial lawyer Isabelle Coutant-Peyre in jail in 2001, has published a collection of his writings from prison in which he expresses his support for Osama bin Laden and heaps praise on Saddam Hussein, calling him the "last Arabic knight".