Before there was Peter Strzok, there was Zip Connolly.

People tend to forget, or maybe never knew, just how corrupt the famous but incompetent Federal Bureau of Investigation has always been. This current scandal is just business as usual for the agency that has metastasized into America’s secret police.

Strzok’s weaselly testimony last week showed just how far off the rails the crooked feds have gone. And it just so happens that this summer is the 40th anniversary of another horrific crime, one in which this same crew of dirty cops played a supporting, but revealing role.

This is a story about another “decorated G-man,” John “Zip” Connolly, currently serving 40 years for a gangland hit in Florida.

Zip will likely be the second gangster/G-man from Boston to end his life in prison, after his FBI mentor, H. Paul Rico, who died in an Oklahoma prison in 2003 as he awaited trial for another underworld murder.

This crime involved a place called Blackfriars, a dank, dark club on Summer Street, where there was always a lot of cocaine and cash. In late June 1978, gunmen invaded the club after hours and shot five men to death during the course of a robbery.

The five murders were never officially solved, but one thing is clear: Whitey Bulger, who was paying off at least seven crooked feds in Boston at the time, did not pull the trigger. But Bulger figured he could still make a score off it.

So he called one of his dirty cops, “special” agent Zip Connolly, and ordered him to get the grisly crime scene photos from the Boston Police Department.

Zip Connolly was puzzled, but hey, Whitey was the boss. Like all the crooked feds, Zip was getting rich off drugs and murder. According to Stevie Flemmi’s court testimony, when Zip collected two $25,000 payments from a drug shakedown, he was ecstatic.

“He says, ‘I’m in the gang.’ ”

Indeed he was. At his retirement dinner, another of the corrupt agents described Zip’s gangster-style dress, featuring “enough gold showing to be the envy of most members of the Gambino Crime Family.”

Anyway, Zip gets the grisly crime-scene photos of the five corpses for his boss. Whitey had a plan. The murdered owner of Blackfriars had a business associate named Teddy Berenson. Whitey figured he was “ripe for an extortion,” as Flemmi put it at Bulger’s trial.

That afternoon, Whitey swaggered into Berenson’s office with a manila envelope. Whitey informed Berenson that he would now pay $60,000 cash to the mob, money that Vincent Solmonte, the club owner, had allegedly owed. Berenson asked why he should be on the hook for the “debt.”

“Because I murdered Solmonte and the others,” Whitey lied. “I have this town tied up. Not only did I kill them all, but I have enough clout that I didn’t even have to leave right away. I stuck around after I killed them.”

Berenson asked Whitey what he meant by that. Whitey opened the envelope he’d brought with him and spread the gruesome photos across his desk.

“He showed him the pictures,” Flemmi recalled in court.

Berenson immediately paid the $60,000 shakedown. Good old Zip — he always earned his paycheck, from Whitey anyway.

The Blackfriars was far from the worst of Zip’s misdeeds. Through the ’80s, he lobbied to keep four innocent men in prison who had been framed for murder by the FBI’s Rico.

Another Boston fed involved in keeping the innocent men in prison for all those years: Robert Mueller, then the U.S. attorney, now in charge of the 13 angry Democrats charged with framing President Trump in the Russian collusion hoax. One of Mueller’s first hires as special counsel: Peter Strzok.

Mueller can recognize that special kind of FBI talent when he sees it. He saw enough of it in Boston over the years.

The worst crime Zip committed, though, was informing Whitey that one of his gunsels was going to rat him out for one of the earlier hits he’d done for FBI agent Rico. Zip was a student at Harvard at the time, but he got a tip from his FBI boss, John “Vino” Morris, another G-man/gangster.

Zip passed the info to his serial-killing master. The would-be rat and another guy were brutally murdered by Whitey on Northern Avenue.

As a reward for his distinguished service as a finger man for the Mob, Vino Morris was then promoted to director of the FBI’s Academy in Quantico, Va. He was in charge of steeping the new recruits in the FBI’s proud “traditions.”

One of the rookie agents who came through in 1995-96 about the time Vino was running the academy was none other than … Peter Strzok.

Do you suppose Vino Morris, who took $7,000 from Whitey for setting up the hit on Northern Avenue, personally instructed Peter Strzok in how to succeed as an FBI agent? Strzok certainly seems to have learned his sordid trade from the best, or should I say the worst, although in the FBI, how can you tell the difference?

Good news for Strzok: Vino Morris is still collecting a pension from the FBI. For his distinguished service as a G-man. No wonder Strzok was sneering Thursday — he’s the very model of a modern FBI agent.

I’ll bet down in prison in Florida Thursday, Zip Connolly was watching Strzok on TV. And no doubt Zip was beaming with pride. The rotten apple doesn’t fall far from the rotten tree.

Read more about decades of FBI corruption in Howie’s books “Ratman” and “Rifleman,” available at howiecarrshow.com.