New York’s powerful Gambino mafia family sent a bomb expert to Sicily to train Cosa Nostra mobsters to assassinate an anti-mafia investigator, a former hitman has claimed.

Maurizio Avola, 56, who is believed to have killed about 80 people before becoming a pentito (informer) told prosecutors in Caltanissetta, Sicily, that an American man came to Palermo in 1992 to help the Sicilian mafia kill the prosecuting magistrate Giovanni Falcone, murdered in a car bomb the same year.

“He was about 40 years old, brown hair, dark eyes, 1.85 metres tall, strong build and dressed very elegantly,” Avola told prosecutors.

Avola said the man was an explosives expert who had worked for the powerful New York gangster boss John Gotti. His job, Avola said, was to train Cosa Nostra’s men to use the 400kg of TNT explosives and a remote-controlled detonator that killed Falcone, his wife, Francesca Morvillo, and three police officers on the road from Palermo to the airport on 23 May 1992.

The ferocious boss Totò Riina had ordered the hit on Falcone as revenge for his investigations, which had led to the arrest of hundreds of mobsters. On Thursday, on the anniversary of Falcone’s assassination, thousands of people paid homage to his memory in Palermo.

It is not the first time Avola has revealed some of the darkest secrets of the Sicilian mafia. Known as occhi di ghiaccio (ice eyes) because of his cold blue-eyed gaze, Avola was recruited as a hitman by the Santapaola family, one of the most feared and powerful in the Sicilian criminal underworld.

He was arrested following a tipoff in 1993, the day after killing a former friend and fellow mafioso. Avola concluded he had been betrayed by his boss, and decided to cooperate with the police, revealing details that led to the opening of new investigations and the arrest of more than 100 mafiosi.

In March 2016, he revealed exclusively to the Guardian that Sicilian mobsters had also planned an ambush to kill Mario Cuomo, the former governor of New York.

Avola said the planned ambush involved about a dozen gunmen armed with assault rifles and explosives.

Targeting a prominent American would send a warning to the law enforcement agencies who had allowed several prominent mafia turncoats to start new lives in the US under assumed identities, Avola said.

Just a few days before Cuomo was due in Messina, the attack was called off.

“The American politician arrived with extremely tight surveillance, lots of bodyguards and a bulletproof car. It made the execution impossible,” Avola said.