French gangster Jacques Cassandri was in court on Monday for a crime committed over 40 years ago. Police cottoned on to the fact that the Marseille mafioso was the likely mastermind of the "heist of the century" after he was discovered to be the anonymous author of a book about the crime.

On July 16, 1976, a group of criminals robbed a branch of Societe Generale, France's third-largest bank, in the southern city of Nice. Using the tunnels underneath the city, the gang was able to partially destroy the floor underneath the bank's basement vault and gain access to the bank notes, jewelry, gold bars and safety deposit boxes located within.

According to the Societe Generale's own account of the incident, the brazen criminals spent the weekend taking their time going through the vault's contents, "even taking the time and luxury to picnic using the depositors' silverware."

On the morning of July 19, the thieves disappeared into the sewers with the 46 million francs (€29 million or $35 million) in loot, none of which was ever recovered.

Police perplexed for 40 years

The case baffled French police for decades. Only one low-level member of the group was caught, and when he named well-known criminal Albert Spaggiari as part of the gang, police assumed he had been the mastermind.

Spaggiari escaped during his 1977 trial in spectacular fashion – distracting the judge with a fake piece of "evidence" and jumping out the courthouse window to a getaway motorcycle. He remained on the run the rest of his life.

It wasn't until 2010 that police began to suspect someone else had orchestrated the heist. Using a pen name, a book was published describing the planning and carrying out of the crime in minute detail.

Investigators were able to deduct that the likely author was Jacque Cassandri, and after a search of his home discovered the manuscript on his computer. He was already well-known to the criminal justice system for being part of the heroin trade in 1970s and for receiving a four-year prison sentence along with his wife in 1994 for pimping charges.

Cassandri confessed to planning the job. He allegedly believed that he could publish the novel because the statue of limitations on the theft had run out – but prosecutors are charging him with laundering the money he stole over the following decades, a charge which Cassandri denies.

Appearing in court on Monday, the now 73-year-old described himself as merely a "pensioner." If convicted, he faces up to 10 years in prison.