America’s notorious Gambino crime family sent an explosives expert to Sicily to help Cosa Nostra blow up a crusading anti-mafia investigator, a turncoat has told Italian prosecutors.

Giovanni Falcone was killed 27 years ago this week, on May 23 1992, when the car he was travelling in was blown to bits by a bomb planted in a culvert beneath a stretch of motorway outside Palermo, Sicily’s regional capital. His wife and three police bodyguards were also killed.

It is still regarded as one of the most heinous crimes in Italy’s history, with the 53-year-old Falcone hailed a hero and regarded as a symbol of the fight against organised crime.

The killing was followed a few months later by the assassination of another high-profile anti-mafia investigator, Paolo Borsellino, who was a close friend and collaborator of Falcone.

It is now claimed that Cosa Nostra, the Sicilian mafia, received training with the bomb and its remote-controlled detonator from an American “man of honour” sent from New York by John Gotti, the notorious head of the Gambino family who was known as ‘the Dapper Don’ for his expensive suits.

“The foreigner arrived in the first few months of 1992,” Maurizio Avola, a convicted mafia killer who became a ‘pentito’ or turncoat in 1994 after confessing to around 80 murders, told investigators recently.