Manhattan federal prosecutors on Wednesday said a Long Island private eye who paid off an NYPD sergeant for information on witnesses “undermined the integrity of law enforcement” and deserved punishment that “recognizes the seriousness of the offense.”

The letter to U.S. District Judge Alison Nathan, who will sentence investigator Joseph Dwyer, 47, of Shoreham, on Friday, didn’t specify that he should do prison time. But the government rejected defense claims that Dwyer acted out of zeal to help the indigent defendants whose cases he was hired to investigate.

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Dwyer, prosecutors said, made $500,000 on billings for indigent defendants from 2011 to 2014, becoming a top investigator because of his ability to get unlawful information, and was “motivated by a desire to enrich himself.”

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Dwyer, a former cop himself and a father of four, is seeking probation. Federal sentencing guidelines call for him to do 10 to 16 months in prison, but probation officials have urged no jail time according to the defense.

Newsday reported Monday that while the bribery case was pending, Dwyer revealed information about a federal informant in a Bronx exoneration case that Manhattan U.S. Attorney Preet Bharara’s office had held back.

That case wasn’t mentioned in prosecutors’ filing Wednesday.