Mafia boss Joseph Massino – and leaders and members of all five families – have just received the most devastating news possible: his brother-in-law and longtime Bonanno family underboss has defected, Gang Land learned yesterday.

Salvatore Vitale, who has been at the pinnacle of New York’s underworld for two decades, was quietly moved into a special unit for turncoats last week after he reached a cooperation agreement with federal prosecutors in Brooklyn, sources said.

Vitale’s decision greatly strengthens the government’s pending case against Massino and his cohorts. Vitale took part in seven mob hits with Massino, according to court papers, and he is also an important potential witness against leaders of other families.

“He fills a big void at the top of the charts,” said one law enforcement official, citing a paucity of high-level turncoats since Gambino underboss Salvatore (Sammy Bull) Gravano and Luchese acting boss Alfonse (Little Al) D’Arco turned on the mob in 1991.

“He (Vitale) knows the current crop of top guys,” the official said, noting that until January, when the Bonanno leaders were indicted and jailed on murder and racketeering charges, Vitale (right) often served as “Massino’s emissary with the other families.”

If Vitale had cooperated sooner, for example, prosecutors could have used him to identify Peter Gotti as the current boss of the

Massino, 60, and Vitale were hit with racketeering and murder charges January 9: Massino for the 1981 murder of Bonanno capo Dominick (Sonny Black) Napolitano, Vitale for the 1992 murder of former New York Post delivery superintendent Robert Perrino.

As Gang Land first reported, the charges stemmed from the first public defections of Bonanno family “made men” – Frank Coppa, Paul Cantarella, and his father, capo Richard (Shellackhead) Cantarella. (left) Shellackhead was charged with Perrino’s murder last year.

The charges were a rude awakening for Massino, who had been unscathed since taking over the family in 1991, while Gambino boss John Gotti and the leaders of the other families were hit with murder and racketeering charges and jailed, some for life.

When Massino was indicted, the feds filed court papers stating that he had suspected that Vitale may have cooperated. Massino feared the worst, the papers said, because Vitale had gotten a “good deal” of 44 months for a 2001 loansharking case and because Vitale was not originally charged with Perrino’s slaying.

Federal prosecutors in Brooklyn refused yesterday to confirm or deny that Vitale is cooperating, but according to Federal Bureau of Prisons records, Vitale, 55, was released from the Metropolitan Correctional Center in Manhattan last Wednesday.

On Friday evening, his lawyer, John Mitchell, received a hand-delivered letter

“Until then, I had no indication that he has apparently decided to cooperate,” said Mitchell, who added that since last Wednesday, he has been unable to reach Vitale or his wife, with whom he previously had maintained frequent contact.

Vitale’s wife Diana, their sons, and other family members were relocated by FBI agents the same day Vitale was transferred out of the MCC, sources said.

In 1987, the brothers-in-law were acquitted of racketeering charges stemming from the undercover work of FBI agent Joe Pistone, a.k.a. Donnie Brasco. Vitale had been charged with hijacking and obstruction of justice; Massino with taking part in three 1980 mob hits that he later admitted to turncoat capo Coppa, (right) according to court papers.

It’s unclear if the feds can use information from Vitale to again charge Massino with those killings – capos Philip Giacone, Dominick Trinchera, and Alphonse Indelicato  – but “we’ll have plenty of options once we debrief Vitale,” said one law enforcement source.

“I’m having difficulty understanding his creatures from the id that would make him cooperate against his brother-in-law,” said Massino’s lawyer, David Breitbart. “The case was ill-conceived, poorly drafted and required someone to cooperate. We only hope that he tells the truth, because that would vindicate Mr. Massino. We know there are many instances, unfortunately, when cooperators are not truthful."