The FBI’s mysterious Big Dig for the cadavers of mob victims on the Brooklyn-Queens border last fall was the result of a tip by its newest high-level informant, Bonanno boss Joseph Massino, Gang Land has learned.

The imprisoned mob boss has been cooperating with the feds since September, sources say, and one of his first information proffers was an empty lot on Ruby Street called “The Hole.” As reporters, TV cameras, and fascinated neighbors looked on for three weeks, the FBI used backhoes and shovels to recover the remains of two capos executed in a 1981 bloodletting by Massino and his cohorts.

Massino had apparently fallen for a bit of mob folklore, however, when he told the feds that the spot was also the final resting place of three John Gotti murder victims, including a Queens man who was killed on orders from the Dapper Don.

The remains of John Favara – a neighbor of Gotti’s who killed the mobster’s 12-year-old son in a tragic accident – were not found during the Big Dig, but the massive undertaking uncovered evidence that capos Dominick “Big Trin” Trinchera and Philip “Philly Lucky” Giaccone had been buried there.

Massino, 62, is the first New York mob boss to publicly violate omerta, the Mafia vow of silence. His extraordinary decision to defect, and to record conversations with his hand-picked acting boss, was disclosed last Thursday. He first reached out to seek some kind of a deal from the feds in September, sources say.

The parameters of his cooperation are not known and it is unclear how extensive and helpful his information will prove to be. But news that the so-called Last Don, a dyed-in-the-wool gangster with supposed Old World mob ethics, is an informer has rocked the underworld, as well as the attorneys and investigators who work for and against gangsters on a regular basis.

“It’s astounding. There are a lot of people who are very worried,” a well-connected mob lawyer told Gang Land.

“Two Gambino old-timers decided they couldn’t take the stress and took a quick trip to Florida,” said one law enforcement source.

A younger, more active, and obviously concerned wiseguy disappeared last weekend, prompting a knowledgeable Gang Land source to quip: “The only guys still around are in jail or on house arrest, and I’m only half-kidding.”

Sources say Massino reached out to the feds two months after he was convicted of seven mob hits. At the time, he was facing mandatory life in prison and the likelihood that prosecutors would seek the death penalty at his pending trial for the 1999 murder of Bonanno capo Gerlando “George From Canada” Sciascia.

Massino’s most obvious goal was avoiding possible execution. He also sought to insure that his wife and other family members did not lose their homes and other possessions as part of the $10 million forfeiture aspect of his racketeering conviction.

In addition to pointing the FBI to a mob graveyard near his and Gotti’s old stomping grounds, sources say Massino furnished some up-to-date information about activities by his and other families as a show of good faith to wary agents and prosecutors under Brooklyn U.S. Attorney Roslynn Mauskopf.

By November 12, when prosecutors Greg Andres and Nicolas Bourtin announced in court that Attorney General Ashcroft had authorized them to seek the death penalty for Sciascia’s murder, sources say that Massino had been providing the feds information for at least six weeks.

A week later, on November 19, the plot thickened. Massino’s hand-picked acting boss, Vincent “Vinny Gorgeous” Basciano,was arrested on murder, arson, and a slew of other charges and added to the Sciascia case. Even though Vinny Gorgeous had no involvement in the Sciascia murder, and Massino was not charged in the same racketeering acts as Basciano, they were co-defendants in the same case and incarcerated at the same federal lockup, the Metropolitan Detention Center in Brooklyn.

On November 23, Vinny Gorgeous proposed the murder of Mr. Andres, the lead prosecutor in their case, to Massino while they were at the Brooklyn Federal Courthouse for a status conference, according to a new murder indictment against Basciano that was filed last week. On December 3, a day that Massino and Basciano attended a co-defendants meeting at the MDC, Vinny Gorgeous told Massino that he had arranged the murder of mob associate Randolph Pizzolo two days earlier, the indictment said.

On two occasions the following month, on January 3 and January 7,Basciano spoke to Massino about the “threat on [Mr. Andres], the murder of Pizzolo and the ongoing and future operations of the Bonanno family,” the indictment said.

While discussing Pizzolo’s killing on January 3, Massino asked: “Why didn’t you just chase him?”

“Because he is a f— dangerous kid that don’t f— listen,” Basciano replied, adding later, “I thought this kid would have been a good wake-up call for everybody.”

Sources say Massino was so eager to please the feds that he agreed to record conversations with Basciano even before his secretly appointed “shadow counsel” had worked out a cooperation agreement with the feds.

In fact, Massino still doesn’t have a signed deal with federal prosecutors.

“It’s a work in progress,” a knowledgeable Gang Land source said.

Massino appeared unshaved and disheveled at a 9 a.m. proceeding before Judge Nicholas Garaufis yesterday. During the brief session, Judge Garaufis officially appointed lawyer Edward Mc-Donald to represent Massino for all purposes, including negotiations with the government regarding his still-pending death penalty case and his sentencing for his racketeering conviction, now scheduled for April 15.

Massino and Mr. McDonald have a history of sorts. During the 1980s, Mr. McDonald headed the federal Organized Crime Strike Force, the elite Brooklyn unit that in 1986 convicted Massino of racketeering charges, the career gangster’s only prior federal rap.

Mr. McDonald, as well as officials with the FBI and U.S. attorney’s office, declined to discuss the confused current status of the turncoat mob boss or exactly how the rights of Basciano and Massino’s other co-defendants weren’t violated by Massino’s dual role as informer and defendant.

The feds made several apparent moves to conceal Massino’s informer status from his former cronies and also blunt future claims that the turncoat boss was a “spy in the camp” of his codefendants.

On November 29, for example, they placed Massino in the MDC’s Segregated Housing Unit, causing Massino to miss a December 10th co-defendants meeting at the MDC. The move also triggered several motions and court appearances by his attorney at the time, Flora Edwards, seeking to return him to general population. Ms. Edwards, who was unaware that Massino was talking to the feds, withdrew as his lawyer when Massino’s informer status became known.

Also, an earlier decision by Massino not to retain his attorney in the July trial, David Breitbart, to defend him for the Sciascia murder seems to have been part of a plan to eliminate the possibility that the veteran trial lawyer would deduce Massino’s dual role.

Lastly, once Basciano’s alleged intention to whack Mr. Andres became known, the prosecutor was removed from that investigation and replaced by another deputy chief in the organized crime unit, Assistant U.S. Attorney Thomas Seigel.