It was a crime mystery combining elements of the films Ocean's Eleven, The Third Man and the 1979 heist movie Sewers of Gold, also known as The Great Riviera Bank Robbery.

Police in Naples had been baffled for months. Six times they were on the verge of capturing would-be bank robbers in the act —- and six times the gang vanished, apparently into thin air.

Three of the aborted raids were even on the same bank, the Antonveneta in the Galleria Umberto I, a smart, wrought-iron-and-glass, art deco shopping arcade opposite the San Carlo Opera House.

When police made arrests yesterday the secret of the gang apparently emerged —- one of those in custody is Salvatore Oliva, the former head of the drains and sewage department for Naples city council.

His knowledge is alleged to have enabled the thieves to melt away into the underground labyrinth of dank, dripping and malodorous tunnels beneath the streets. Police said that the gang had 22 members.

Their technique was allegedly the same in every case: they rented ground-floor rooms next to the banks and when the bank employees had departed, dug tunnels at nights and weekends into the vaults containing safe deposit boxes.

The robbers' plan, which nearly came off, was to ensure that their tunnels connected to the sewer system so they could use it as an escape route. They even used a computer to create a model of the intricate network.

In the last raid on the Antonveneta in February the police, acting on a tip-off, were waiting inside the bank as the robbers emerged - but the gang leapt back into the tunnel and disappeared into the drains.

“No one knows more about underground Naples than Oliva,” a police spokesman told Il Mattino, the Naples newspaper. “He could navigate it with his eyes closed. He knows where all the drains are: the water mains; the dangerous electrical cables.”

Other alleged members of the gang under arrest include three police officers who were to act as lookouts —- in uniform —- then conceal the loot, which the robbers calculated would amount to more than 100 million euros (£80 million).

During one abortive raid the policemen were spotted by patrolling colleagues but they assured them that they were on official duty and “everything is in order”.

Two private security guards also allegedly advised the robbers about the type of security alarms used by the banks so that they could be neutralised by gang members, who were recruited for their expertise in security and communications systems.

After a six-month police operation the secret of the gang was uncovered when the investigators —- headed by Vittorio Pisani, the deputy head of the Naples police, and Massimo Sacco, the head of the anti-robbery flying squad —- intercepted mobile phone calls in which gang leaders were overheard asking a local Mafia boss for his permission to carry out the raid on his patch.

He agreed —- provided he was given a share of the proceeds.

Police said that the robbers used the names of footballers, including Luís Figo, Gennaro Gattuso and the Napoli player Emanuele Calaiò, as aliases in an attempt to disguise their identities when making phone calls.

In The Third Man, the film directed by Carol Reed which was set in the bombed-out ruins of postwar, occupied Vienna, the black-market racketeer Harry Lime eludes his pursuers by hiding in the sewers of the city, but in a famous chase scene he is tracked down eventually and shot.

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