The Nassau district attorney’s office has closed the final chapter of its criminal investigation into a politically charged arrest that forced former police Commissioner Thomas Dale and former Chief of Detectives John Capece to resign two years ago.

A spokesman for incoming Nassau District Attorney Madeline Singas said Thursday that no criminal charges will be filed against former Sgt. Sal Mistretta, who served a subpoena on Randy White while the campaign worker was in police custody.

DA spokesman Shams Tarek said, “Our investigation into the arrest and subpoenaing of Randy White, conducted alongside the Police Department’s Internal Affairs Unit, revealed troubling activity that while not provable to be criminal, led to the resignation of the county’s police commissioner, the county’s chief of detectives and the sergeant who served Mr. White.”

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Mistretta, who retired in November 2013 after 26 years on the job, said Thursday, “I am happy that the facts of this case have vindicated me. Many people from all walks of life have specifically come to my defense and I appreciate their support.”

Former District Attorney Kathleen Rice began investigating when three police officers pulled White off a public bus in Roosevelt after he had testified in a 2013 election case, arresting him on an unrelated $250 misdemeanor warrant.

White had testified that he had been paid illegally to collect nominating petitions for the county executive campaign of former Freeport Mayor Andrew Hardwick. Hardwick, whose failed third-party campaign was financed by political power broker Gary Melius, denied the allegation.

Rice said in a December 2013 report that White was arrested at the direction of Dale and Capece after Melius called Dale, saying he wanted to file perjury charges against White.

Rice found no criminal wrongdoing but said she was continuing to investigate the serving of the subpoena.

Mistretta, who was off duty at the time, told Newsday he did not know the paper he gave White was a subpoena.

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During the two-year investigation, Mistretta said, “I didn’t stop my life. I had one book regarding gun control published this year which has been a success.”

Mistretta, who ran the police department’s pistol license bureau, released a book this summer titled “Gun Control for Bad Guys, Gun Solutions for Good Guys.”

Rice’s initial findings of no criminal wrongdoing created a deep break in her relationship with Nassau Democratic chairman Jay Jacobs, who publicly questioned why she didn’t file charges.

Jacobs supported Singas, who served as acting district attorney after Rice was elected to Congress, in the district attorney’s race this year.

“I know that this district attorney made every effort to determine whether there was sufficient evidence to bring an indictment,” Jacobs said Thursday. “The fact that there was no indictment is more a function of a lack of evidence needed for conviction than a lack of wrongdoing on the part of those who pulled Randy White off that bus over two years ago.”