At least three investigators with the Suffolk district attorney’s office have been subpoenaed as a federal investigation has expanded into whether county investigators and prosecutors engaged in federal civil rights violations by illegally using a wiretap, sources say.

The subpoenas were issued by a federal grand jury in Central Islip that has been probing the use of a wiretap as a new part of its overall investigation into the possible illegal conduct of Suffolk law enforcement officials, the sources said.

The wiretap was placed in 2014 on the phone of then-Suffolk Det. John Oliva, with the approval of a state Supreme Court justice, because he was suspected of leaking information on a robbery case, the sources said.

But the jury is probing whether the wiretap requested by the office of District Attorney Thomas Spota was actually aimed at obtaining details about the people Oliva was talking to and what types of information he was providing. Oliva was known to be close to federal agents and prosecutors, who had been investigating then-Suffolk Chief of Department James Burke, the sources said.

It can be a civil rights violation if a wiretap is used to obtain information that goes beyond the scope of what the judge approved. In addition, investigators are not supposed to record the parts of conversations that did not pertain to the wiretap’s original purpose.

The grand jury indicted Burke in December for allegedly beating a drug dealer who stole a duffel bag from the chief’s department SUV and then obstructing justice by masterminding a cover-up of the attack.

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Burke, who is being held without bond, has pleaded not guilty. Federal prosecutors recently revealed that they have offered a plea deal to him. Joseph Conway of Mineola, Burke’s attorney, said they were examining the offer but anticipated going to trial.

Newsday reported last month that the grand jury also has sent a letter to Christopher McPartland, the head of the district attorney’s governmental corruption and public integrity unit, informing him that he is a target of the grand jury investigation. Sources have said that the grand jury was looking into whether McPartland was involved in obstruction of justice as an outgrowth of the Burke case.

A target letter is an indication that the grand jury suspects the recipient might be involved in wrongdoing and is designed to warn the person against self-incrimination by testifying. But the letter does not mean the grand jury is about to charge the person with a crime.

Pulled over officer’s car

The three investigators who were subpoenaed report to McPartland and were among those in the district attorney’s office involved in monitoring the wiretap on Oliva’s phone. Two of those investigators eventually pulled Oliva’s car over in 2014, confiscated his cellphone and unsuccessfully attempted to get him to accompany them to a confidential site where the district attorney’s office conducts sensitive investigations, the sources said.

Anthony La Pinta of Hauppauge, an attorney for Thomas Iacopelli, one of the two district attorney’s investigators involved in the Oliva car stop, declined to comment. Kevin Snover of North Babylon, an attorney for Paul Caroleo, the other investigator involved in both the wiretap monitoring and the Oliva stop, did not return calls for comment.

David Besso of Bay Shore, the attorney for the third subpoenaed investigator, declined to comment. The name of the third investigator could not immediately be confirmed.

Robert Clifford, a spokesman for the Suffolk district attorney’s office, and Nellin McIntosh, a spokeswoman for the Office of the U.S. Attorney for the Eastern District, both declined to comment.

Spota has not been accused of any wrongdoing.

In successfully seeking to have Burke held without bail as a danger to the community, federal prosecutors alleged that Burke and an unnamed person failed to report an accident in which a drunken Burke smashed into a state car driven by the unnamed person. Sources have identified the other person as McPartland.

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McPartland’s attorney, former federal prosecutor Lawrence Krantz of Manhattan, did not return a request for comment on the subpoenas to investigators. He has previously declined to comment on his client’s receiving a target letter.

The wiretap investigation ran for 17 weeks, the sources said. The length of time the wiretap went on and when it occurred raised the suspicion of federal investigators, the sources said.

It is unusual for law enforcement officials to devote that much staff and time to a single robbery, the sources noted, particularly when Suffolk was facing drug and gang problems, as well as homicides, and all the unsolved cases of the bodies found at Gilgo Beach.

Oliva was removed, along with another Suffolk detective, by Burke in 2012 from the FBI’s joint Long Island Gang Task Force in an action that caused something of a firestorm. Burke said at the time that the reason was to concentrate county anti-gang efforts on the local level, but critics asserted it was because Burke and Spota believed federal officials were hogging credit for gang cases.

All kinds of conversations

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The wiretap picked up all kinds of conversations Oliva had, both professional and personal, including ones with a Newsday reporter, and many with federal prosecutors and FBI agents, whom Oliva had worked with on the task force, the sources said. Some of the conversations involved gossip about Burke’s alleged actions, they said.

Retired Suffolk Det. Sgt. Robert Doyle, the former head of the police’s Major Crime Bureau and an Oliva supporter, has said the district attorney’s wiretap was unusual.

“In 37 years in every investigative command, I never knew of a wiretap investigation into leaks,” Doyle said. “This was to expose the people who were talking negative about him [Burke].”

Eventually, Oliva acknowledged he had provided information to a Newsday reporter. Not about the robbery case — in which arrests had been made weeks before the wiretap even began — but information that he believed showed the department was downplaying gang violence after he had been removed from the task force, the sources said.

Oliva resigned from the police force in September 2014, pleaded guilty to the misdemeanor of official misconduct and received a conditional discharge.

“I am deeply troubled and saddened by the conduct of the defendant in this case, who acted without regard for the consequences of his behavior on the safety of his fellow officers, and on serious, pending criminal investigations,” Spota said on the day of Oliva’s plea.

Conviction for illegal use of a wiretap could amount to a federal civil rights violation. Criminal violation of civil rights can carry sentences of up to 10 years in prison; illegal wiretapping up to 5 years.