New York ? For 23 years, it was an unsolvable crime: a mob hit on three Bonanno family captains, slaughtered by machine gun fire in a social club.

The details finally spilled forth this summer as the family’s ex-underboss, now a government informant who remembered everything but the definition of “omerta,” implicated Bonanno chief Joseph “Big Joey” Massino.

Thanks to a seemingly endless parade of Mafia turncoats, prosecutors are indicting and convicting mobsters on crimes dating back decades.

The latest example was the indictment this past week of John A. “Junior” Gotti for an alleged 1992 botched attempt to kill talk radio host Curtis Sliwa over slurs directed at the mobster’s father, the one-time head of the Gambino crime family.

The link to Gotti reportedly came from a former Gambino family capo, Michael “Mikey Scars” DiLeonardo.

“It’s the critical difference,” former federal prosecutor Jim Walden said of informants. “Without the testimony from these insiders, many of these cases against the Mafia would never have happened.”

Walden knows firsthand. In 2001, using 10 cooperating witnesses, he won a conviction against Bonanno family “consigliere” Anthony Spero for murder, gambling and loansharking.

In the Massino case, where closing arguments were heard this past week, the alleged crimes date back even further. One of the eight turncoat witnesses against him was his own underboss and brother-in-law, Salvatore “Good Lookin’ Sal” Vitale. The two had a friendship that began when they were teens, and Vitale, who has confessed to 11 murders, said Massino taught him everything he needed to know about organized crime.

“Thirty years ago, a case this like was not possible,” said Ronald Goldstock, former head of the New York state Organized Crime Task Force. “The first cases with informants were in the early ’80s.”

By the ’90s, the trend of ignoring omerta, the mob’s oath of secrecy, was in full swing.