Michael Scotto, a Port Washington native who spent more than two decades as a prosecutor in the Manhattan district attorney's office, will declare his candidacy for Nassau County District Attorney today at a news conference in Mineola.

Scotto will challenge Acting District Attorney Madeline Singas in the Democratic Primary in September. The party is backing Singas.

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"I'm an outsider, not a politician," said Scotto. "Voters deserve a real choice for DA and should not have to settle."

Scotto, 50, worked for the Manhattan district attorney's office for 22 years. He worked first as an assistant district attorney prosecuting violent street crime, and later as chief of the labor racketeering unit and rackets bureau, where he handled cases involving organized crime and elected officials accused of trying to rig government contracts.

Scotto left the office in 2012 and now runs a private law practice in Garden City.

The Nassau GOP Wednesday night is expected to nominate Hempstead Town Supervisor Kate Murray as its candidate.

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Singas' campaign declined to comment.