Mob music: How the creators of the Jersey Boys got a call from the Mafia

While other jukebox musicals have taken the route of hagiography (Buddy) or fantasy (Mamma Mia), Jersey Boys is a little bit different. Instead of using The Four Seasons' catalogue to illustrate the triumph of talent and persistence, or a fictional romantic romp, Rick Elice and Marshall Brickman fashioned what The New York Times called "a no-holds-barred band biography". Not only is it frank about the quarrels, betrayals, and sexual rivalries of the early Sixties doo-wop group, it also shows, for the first time, that Tommy DeVito, Nick Massi, Bob Gaudio, and Frankie Valli (né Castelluccio) had their brushes with the Mafia.

The boys whose soaring harmonies propelled "Sherry", "Big Girls Don't Cry" and dozens of other songs up the charts were not unusual in this respect among the citizens of New Jersey, the most notoriously corrupt of the 50 states. Organised crime may permeate Jersey life at every level – DeVito recalled that he would come across three or four craps games on the way to church, and there would sometimes be gambling in the church basement too – but the wealth does not trickle down to the mainly working-class populace. So, as DeVito tells us at the outset of Jersey Boys, "If you're from my neighbourhood, you've got three ways out – you could join the army, you could get mobbed up, or you could become a star." But you could not become a star in New Jersey nightclubs without the cooperation of the Mafia, which ran not only the clubs, but the food, drink, and linen companies that supplied them.

Valli, he of the thrilling falsetto, is proud, says Elice, that "he managed, as an Italian entertainer, not to be owned or controlled by a Mob family" – any crimes he committed being merely fictional ones when he played a gangster in several episodes of The Sopranos. And Gaudio, who wrote the group's music, never took part in any illegal activities, though that took some doing. Elice recalls that Gaudio bought his father a Chinese restaurant, to which, one day, a cigarette machine was delivered. "Bob got on the phone and called somebody who called somebody, who had it taken away. He knew that the next thing would be demands for protection."

DeVito, however, was a cocky type who, according to Elice, revered Sinatra less than he did Al Capone. He loved hanging out with mobsters, had been involved in petty crime since childhood, and, along with his brother (an early member of the group) and Massi, had spent time in prison, where he learned to play the guitar. When Valli is shaken down by two hoodlums, he appeals to DeVito, who tells us, "You wanted something done – or undone – in New Jersey, Gyp DeCarlo was the man."

Specifically, Angelo "Gyp" DeCarlo was the man who ran the DeCavalcante family's loan-sharking and illegal gambling operations in New Jersey. He died in 1973, but left associates who were keen to defend his reputation. When Elice and Brickman were trying out the show in a California theatre, they got a message that someone wanted to speak to them on the telephone in the car park. A man who did not give his name said that he had heard DeCarlo appeared in the show, and wished to ensure that he was portrayed in a favourable and respectful manner. Marshall Brickman says there was only one answer: "Of course!"

DeCarlo is indeed portrayed in a respectful and favourable manner – as a wise, kindly counsellor who helps the band with their problems. One of these is DeVito's inability to repay the extortionate interest, or "vig" (short for "vigorish", from the Yiddish for "profit"), on his debt to the moneylender Norm the Bag, thereby risking the loss of important anatomical features. Gyp makes sure he doesn't get hurt – behaviour that was highly uncharacteristic for the real DeCarlo, a multiple murderer.

One debtor who got behind on the vig was badly beaten, then suddenly died of a stomach upset that turned out to have been caused by considerable quantities of arsenic. While the Four Seasons were recording their hits, DeCarlo was unwittingly doing some singing of his own – to the FBI, which bugged his headquarters for several years in the early Sixties. He was heard describing how he hit one victim with a gun butt and crowbar before setting fire to him, and how, feeling more sympathetic to another, he told him to stop struggling so he could take a clean, painless hit through the heart.

Convicted of extortion and conspiracy to commit murder, DeCarlo haughtily uttered the classic line: "It was a frame-up." But if that made listeners howl, it was DeCarlo who had the last laugh. Less than two years into a 12-year sentence, he was pardoned by President Nixon after Sinatra made a large contribution to Nixon's re-election campaign. While he was in the Atlanta penitentiary, The Four Seasons flew down to play a concert for the prisoners.

Why not put this in the show? "Because that's not what the show is about, just like it's not about the space programme or the opening of the West," says Brickman. "It's not The Sopranos set to music. We thought it would be counterproductive to introduce that level of reality." Elice concurs, saying that the phone call did not change anything. "Whatever else he [DeCarlo] did, he was a good guy to The Four Seasons."

DeVito's troubles did not end when his loan was sorted out, or even after he was removed from the group and, at DeCarlo's mandatory "suggestion", from New Jersey. "Even when Tommy wasn't hurting for money," says Brickman, "he would do a little counterfeiting, a bit with bearer bonds. It was a habit." He has lived for some time in Las Vegas, working for another graduate of the old neighbourhood, Joe Pesci.

The scene in Jersey Boys that seems too much of a cliché to be true is, say the writers, one of those things that's a cliché because it's true. The writers have stuck to the facts in portraying DeCarlo's sentimental side, whatever its lack of objective correlative: he dissolves in tears when Valli sings, at his request, "My Mother's Eyes" ("One bright and guiding light/ That taught me wrong from right"). The song fits the story because Valli had, early in his career, recorded it, but, in fact, DeCarlo's favourite song was more subtly ironic. According to the singer Jimmy Roselli, DeCarlo, while driving, would croon "I Lost All My Love for You", which includes the lines: "Revenge may be sweet after all I've been through/ But why should I hurt you? What good would it do?" If anyone is thinking about a musical version of The Sopranos, that could be a good place to begin.

'Jersey Boys' is at the Prince Edward Theatre, London W1 (0844 482 5138) to 18 October