The long-awaited “Mafia Cops” case opened with a bang this week as a pair of aging mob turncoats with keen memories took the stand in Brooklyn Federal Court to finger ex-detectives Louis Eppolito and Stephen Caracappa as calculating, cold-blooded killers for hire.

As damning as the testimony of onetime Luchese acting boss Alfonse D’Arco and renegade mob associate Burton Kaplan sounded, the most powerful witness against the former cops could be a name and number found in a little pocket address book in a dusty old homicide file by detective investigators who just wouldn’t quit working the case.

The address book itself may never surface in the trial, but Gang Land has learned that it led probers to the discovery of a crucial eyewitness to the first hit allegedly carried out by the duo. That witness will be among the 10 so-called civilian witnesses the feds expect to call to the stand to tell what they know about the cops and the slayings of eight men between February 1986 and November 1990 to corroborate the testimony of D’Arco, Kaplan, and other admitted murderers and longtime criminals.

The most important civilian testimony, according to the opening remarks of Assistant U.S. Attorney Mitra Hormozi, will be that of Peter Franzone, a hardworking family man with a sixth-grade education who was terrorized into digging a grave for a slain diamond merchant, Israel Greenwald.

Yesterday, Kaplan testified that he paid $30,000 to Mr. Eppolito; the detective’s cousin, Frank Santora, whom Kaplan had met in prison, and to Mr. Caracappa for the murder of Greenwald, whose name he couldn’t recall. The jeweler, whom Kaplan had dragged into a stolen Treasury bill scheme, had become a target of Interpol, and Kaplan feared he would cooperate with authorities and help send Kaplan back to prison.

On February 10, 1986, Ms. Hormozi told the jury, Mr. Franzone, who owned a towing business and did repair work on the side, saw Mr. Eppolito and Santora drive into a Brooklyn parking lot/garage he managed and park their car facing out. Mr. Franzone knew both men. He had done some work on cars for Santora, and had met Mr. Eppolito though his cousin.

Mr. Eppolito remained in the car, Ms. Hormozi said. Mr. Franzone saw Santora and a “thin man he later recognized to be Caracappa” pass his office and lead a man “wearing a yarmulke, the skull cap of an Orthodox Jew,” into an enclosed single-car garage and close the door behind them. Minutes later, the door opened, and Santora and Mr. Caracappa walked out of the parking lot. Mr. Eppolito drove off.

Soon after, Ms. Hormozi said, Santora drove his white Cadillac into the lot, walked into Mr. Franzone’s office, and escorted him to the garage: “When they opened the garage door, Franzone saw Greenwald slumped over dead. Santora ordered Franzone to help him dig a grave for the dead man. Franzone was shocked. Santora was merciless.

“‘You’re part of this. You’re an accomplice,’ he told him. ‘Start digging or I’ll kill your family. Start digging or I’ll kill you.’ Franzone was terrified. He knew that Eppolito was a New York City detective. He knew that Santora was a killer. He knew they had just killed a man at his garage. Whom could he go to? What could he do? He helped,” she said.

Ms. Hormozi told jurors that forensic anthropologists who examined Greenwald’s remains after they were dug up last April will confirm the testimony of Mr. Franzone and Kaplan.

“Greenwald was found with a plastic bag over his head,” she said. “He was shot twice in the back of the head. He was wearing a blue pin-striped suit. He had a watch where his wrist would have been. He still had his wallet with his ID in his pockets. He still had the remnants of a yarmulke by his skull.”

Kaplan implicated the accused Mafia Cops in the jeweler’s murder at the same time he confessed to others in which the cops were allegedly involved. But investigators could not obtain any corroborating evidence until after the ex-detectives were first hit with racketeering and murder charges in March of last year.

Unlike the other slayings – Mr. Caracappa is linked to 11, Mr. Eppolito to 12 – former Luchese underboss Anthony “Gaspipe” Casso had nothing to do with Greenwald’s murder and did not tell the FBI about it when he began cooperating in 1994.

And the only provable specifics Kaplan could recall getting from Santora – he was killed in an unrelated mob hit in September 1987 – was that it happened in a garage on Nostrand Avenue.

That gibed with an important fact that Casso had mentioned about the kidnap/torture killing of James Hydell, a Gambino associate whom “the cops” had abducted and turned over to the mobster in October 1986. A garage on Nostrand Avenue was where “the cops” transferred Hydell to the trunk from the backseat of the car they later delivered to Casso, according to FBI reports obtained by Gang Land. But Nostrand Avenue is several miles long, running from Sheepshead Bay to Williamsburg. Locating the garage would be like finding a needle in a haystack.

Detective investigators with the Brooklyn district attorney’s office, which was part of the state-federal task force investigating the rogue detectives at the time, narrowed the location down to Mr. Eppolito’s old precinct, the 63rd, but they could get no further.

Stymied but undeterred, they redoubled their efforts and finally located the original Santora homicide folder with the entire file on the double murder of Santora and Carmine Varriale. Ironically, according to FBI documents, the gunmen who killed them had been dispatched by Gaspipe Casso to whack Varriale, the object of his disaffection then.

Among the ballistics and medical reports and other papers, the investigators found what they needed – a telephone book that Santora had in his pocket when he was killed. They found a phone number, and an address, 2232 Nostrand Ave., for Pete’s Towing.

Nineteen years earlier, Ms. Hormozi told the jury, Mr. Franzone had “felt that he was digging his own grave as well.” When he was approached by law enforcement last year, he panicked, but after he checked with an attorney, she said, “Pete Franzone unburdened himself. He pointed to a spot, and after rotting in a cold, dark grave for 19 years, Israel’s body was exhumed.”

It’s unclear whether Mr. Franzone also has linked his parking garage to the slaying of Hydell. But, according to Ms. Hormozi, the feds have another civilian eyewitness prepared to testify that she saw Messrs. Eppolito and Caracappa come to his house looking for him the same day he disappeared.

“On October 18, 1986, the defendants drove by Hydell’s house in Staten Island and actually spoke to his mother, Betty Hydell,” she said.

Kaplan laid the groundwork for Betty Hydell’s appearance yesterday by testifying that a year or two after her son’s abduction, Mr. Caracappa recalled how he and Mr. Eppolito had worked doggedly to find Hydell: “He said they had gone out to Staten Island and asked his mother where Jimmy was.”

This column and other news of organized crime will appear later today at www.ganglandnews.com.