A Gambino wiseguy who fired the fatal shots in one of the last rub-outs ordered by the late John Gotti has turned on the mob, and will testify about the killing at the racketeering trials of Peter Gotti and John A. “Junior” Gotti, Gang Land has learned.

Frank “Frankie Fapp” Fappiano, a member of a seven-man hit team that killed mob associate Edward Garofalo in front of his Bensonhurst, Brooklyn home on August 8, 1990, recently became the family’s fourth “made man” to defect, sources said.

Fappiano, 42, has never risen above the rank of soldier, but law enforcement officials tell Gang Land they expect big things from the former Teamsters foreman.

“Fappiano has plenty of information the federal government can use in addition to his testimony at the two Gotti trials,” one law enforcement source said.

His testimony about the slaying will be the first by a member of the Garofalo hit team, even though the leader of the crew – former superstar prosecution witness Salvatore “Sammy Bull” Gravano, the family’s first turncoat – gave authorities the identities of the entire hit team in 1991.

Surveillance conducted before and after the killing backed up Gravano’s tale, but no charges were lodged because the feds made an agreement with Sammy Bull not to use him as a witness against members of his crew.

A few days before the killing, Gravano had said, Fappiano and two other hit team members, Thomas “Huck” Carbonaro and Joseph “Little Joe” D’Angelo, had ironed out details of the hit with him and the Dapper Don at his Little Italy social club. On August 2, 1990, FBI videotapes captured all of them together in front of the Ravenite Social Club.

The afternoon of the murder, Sammy Bull, Frankie Fapp, and his then-brother-in-law and mob supervisor, Michael “Mikey Scars” DiLeonardo, were spotted and photographed on a “walk talk” near Gravano’s construction company office.

The day after the killing, six suspects -Fappiano, Carbonaro, D’Angelo, Louis “Big Lou” Vallario, Gravano, and his brother-in-law Edward Garafola – were photographed in animated discussion outside Gravano’s office by investigators with the state Organized Crime Task Force.

At Junior’s trial, sources say, Frankie Fapp will be a key witness against D’Angelo, a soldier who also is charged with being the wheelman in the ambush shooting of radio talk-show host Curtis Sliwa that Junior allegedly ordered.

Sources say Fappiano will also corroborate much testimony by DiLeonardo, who began cooperating two years ago and helped federal prosecutors in Manhattan jump-start the grand jury probe that led to the indictment charging Junior with ordering the attempted murder of Sliwa in 1992. Mikey Scars and Frankie Fapp were photographed with Junior on a gambling junket to Foxwoods in the mid-1990s, according to court records.

At Peter Gotti’s trial, Fappiano will testify that Carbonaro, who drove a “crash car” during the Garofalo hit, and Garafola – a relative of the murder victim who spells his name differently – were also members of Gravano’s hit team.

Fappiano is also slated to testify that Peter Gotti supervised various extortion activities in the construction industry while he served as a capo, boss, or acting boss from the mid-1990s until last year, and received a share of the payoffs, sources said.

For that, Peter Gotti has only himself to blame.

On August 27, sources said, Gotti squashed a so-called “global plea bargain” deal that would have resolved the case for all defendants. He rejected his deal, even though it was for the least amount of time possible.

The charges and the evidence against each are different, but here are the numbers and prison time they face on other convictions. Fappiano was offered 25 years. So was Carbonaro, 56, who faces 10 years for a Brooklyn murder conspiracy conviction. Mob associate John Matera, 34, who still has two years to serve for a Brooklyn conviction; 20 years. Garafola, 66, was offered 15 years. Gotti, 64, who has seven years remaining for his Brooklyn conviction, was offered a “guidelines” plea that called for 12 to 15 years.

As the deadline approached, sources said, Fappiano and Gotti were still playing hardball. Facing a certain life sentence if convicted, Fappiano was holding out for 20 years. Gotti, who faced 70 years, was, in the words of one source, “looking for a light at the end of the tunnel.”

Eventually, sources said, Fappiano caved in and took the 25-year offer. Gotti, as he had done in his racketeering case in Brooklyn last year, turned his down.

Later that night, prison officials took Frankie Fapp from a general population unit at the Metropolitan Correctional Center and placed him in a segregated unit to await a transfer to a secure unit for cooperating witnesses, and his own possible light at the end of the tunnel.

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Fappiano’s decision to cooperate is likely to establish once and for all that he, and not Gambino associate Daniel Fama, the seventh member of the Garofalo hit team, was the gunman who whacked the wealthy demolition contractor.

Sources say Fappiano has owned up to being the triggerman, a role Gravano also credited to him.

According to an FBI report, Fama told Frank Gioia Jr., a Luchese soldier with whom he dealt heroin in the early 1990s, “At the time of the hit, Fappiano was nervous.” Fama boasted that he had done the dirty deed and that Fappiano had driven the getaway car.

Fama claimed that many Gambino mobsters considered Frankie Fapp a gutless “dog,” who didn’t deserve to be a made man.

Fama, 40, is scheduled to complete a 15-year federal prison sentence for drug dealing in 2009. These days, if forced to comment, Fama would surely agree with Fappiano’s version of the killing.