Art lovers in Sicily are appealing to a mafia informer serving a life term in prison to reveal the hiding place of a stolen Caravaggio worth an estimated 20m. They believe Francesco Marino Mannoia knows the location of the Nativity with Saints Francis and Lawrence, which was cut from its frame in the San Lorenzo oratory, Palermo, in 1969. Mannoia, a heroin refiner whose mother, sister and aunt were murdered by the mafia after he turned state's evidence, has admitted taking part in the theft. He has revealed that the painting was damaged but has never given any clues to its location. Palermo's artistic heritage societies, who have organised a new campaign for the Caravaggio's return, want Mannoia to help. "We cannot offer him anything for this information but we are appealing to his conscience. It is something he could do for the good of Sicily," said Riccardo Agnello, head of the Palermo branch of the Italian Environment Fund. The work was painted by Caravaggio in 1609, a year before he died. The Italian police, Interpol and the FBI have all tried to trace it and the painting has acquired mythical status. Theories abound as to its fate: it was destroyed shortly after the theft, it was sold to a collector in eastern Europe, it was buried in an earthquake in Naples or it remains in mafia hands. Mr Agnello and his fellow campaigners believe the painting was too hot to handle and remains in Sicily. "A carpet was taken on the same night and we believe the Caravaggio is still rolled up in that carpet and hidden somewhere between Palermo and [nearby] Bagheria," he said. More than 1,000 people in the city have signed a petition asking the underworld for information