A four-month law enforcement investigation has shut off a heroin pipeline that stretched from Pittsburgh to New York City and Long Island, netted seven arrests, and kept up to $1 million in narcotics from hitting the streets, authorities said Monday.

Some of the heroin seized by investigators was more than three times as pure as what would normally be on the street, Nassau District Attorney Madeline Singas said at a news conference, dubbing the product “exceptionally deadly.”

The arrests and indictments followed an investigation by Nassau police, prosecutors and a U.S. Drug Enforcement Administration task force, with help from other agencies including New York City’s special narcotics prosecutor and Port Authority police, Singas said.

“We will continue to make sure that the people who are pushing this poison on our streets will be held accountable,” Singas said.

Law enforcement officials said Victor McKeever, 53, of Pittsburgh, was the ring’s leader. He ran the operation from his home and used a Queens stash house to attempt to funnel about 3.5 kilograms of heroin to locations including Freeport in Nassau County, authorities said.

Nassau Executive Edward Mangano, left, Nassau District Attorney Madeline Singas and acting Police Commissioner Thomas Krumpter, right, display heroin recovered in an investigation Monday. Photo Credit: Howard Schnapp

Acting Nassau Police Commissioner Thomas Krumpter said that perhaps most troubling, the drug fentanyl — also seized along with $90,000 in cash — was used as a heroin cutting agent.

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“When you add fentanyl into heroin,” Krumpter said, “the likelihood of a fatal overdose or an overdose is exponentially greater.”

Besides McKeever, those also facing a charge of operating as a major drug trafficker are: Donna Peart-Martin, 51, of Freeport; Mark Mahabirsingh, 34, of Queens; and Tariq Johnson, 39, of Englewood, New Jersey.

Each of the four faces up to 25 years to life in prison if convicted of the felony. All defendants have pleaded not guilty in Nassau County Court.

On June 9, McKeever appeared in court in Mineola before a judge set his bond at $1 million. Authorities had arrested McKeever in December, before he unsuccessfully fought his extradition last week from Pennsylvania.

“He says he has absolutely nothing to do with these charges and these events,” defense attorney Jason Russo of Bay Shore said Monday.

Johnson’s attorney, Mahmoud Rabah of Forest Hills, said Monday that his client denies the allegations and he fully expects Johnson’s interests “to prevail in court.”

Authorities said detectives tailed some of the suspects and used electronic surveillance, leading to a Nov. 22 seizure of about two kilos of heroin — worth around $600,000 — at a Megabus depot in Manhattan.

Investigators later found the network’s stash house in a Kew Gardens apartment, leading to a Dec. 9 seizure of about another kilo of heroin and the arrest of Shawn Patterson, 49, of North Charleston, South Carolina, authorities said.

Patterson had about 400 grams of heroin on him, according to authorities, but his lawyer, Scott Brettschneider of Forest Hills, said Monday there’s no evidence connecting Patterson to the drug conspiracy.

Prosecutors identified the other drug ring suspects as: Anthony Greer, 25, of Pittsburgh; and Ebony Felder, 32, of the Atlanta area.

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An attorney for Greer, who’s facing charges including first-degree criminal drug possession and conspiracy following his April arraignment, declined to comment Monday.

Felder was arraigned Monday on felony conspiracy charges. That followed her extradition from Georgia, which Garden City defense attorney William Kephart said the nursing facility worker didn’t contest.

Authorities identified Peart-Martin and Mahabirsingh as the ring’s alleged local drug distributors.

Mahabirsingh’s attorney, Robert DiDio of Kew Gardens, said his client had won a significant bail reduction and was vigorously fighting the charges.