Nassau County Executive Edward Mangano testified last week before a federal grand jury looking into allegations against state Sen. Dean Skelos (R-Rockville Centre), Long Island's highest-ranking legislator and the Senate's majority leader, and his son, sources said.

Mangano was among several Nassau politicians subpoenaed to testify, the sources said.

The New York Times reported Wednesday that prosecutors with the office of Preet Bharara, the U.S. attorney for the Southern District of New York based in Manhattan, were investigating Skelos and his son, Adam, citing unnamed sources.

Bharara's office is looking into a payment to Adam Skelos for as much as $20,000 by a title insurance firm for which he never worked, as well as the awarding by Nassau County of a contract to a firm where Adam Skelos was on the payroll, the paper reported.

The firm, AbTech Industries of Scottsdale, Arizona, had received a county contract for storm water treatment although it was not the lowest bidder for the project, according to the report. In July 2014, Mangano issued a news release touting the merits of the treatment's technology, calling it a "major step forward" in protecting the environment.

The sources said Mangano was asked about various Nassau County contracts. Mangano did not appear to be a target of the investigation and there was no suggestion he had done anything wrong, the sources said. He was questioned mostly about procedures and facts, such as what contracts had been let and who had bid on them, the sources said.

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Attempts to reach Mangano and his spokesman, Brian Nevin, were unsuccessful late Wednesday night.

A call to the senator's home Wednesday night was answered by a woman, who, before hanging up, said Skelos wasn't there.

Reached at his Rockville Centre home, just blocks away from his father's, Adam Skelos said, "Any questions you have, you can direct them to my attorney." His lawyer, Christopher Conniff, didn't immediately return messages Wednesday night.

An FBI official and a spokesman for Bharara had no comment Wednesday night.

Prosecutors are examining if any dealings constituted a conflict of interest for Dean Skelos, and whether he, as a top state legislator, intervened in matters concerning AbTech and another firm, Glenwood Management, which has had close ties to AbTech, the Times reported.

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Another firm, Newport Engineering, had submitted a substantially lower bid, according to the Times report. That company's head could not be reached Wednesday night.

According to AbTech's website, the storm water treatment contract was awarded in October 2013. The county's commissioner of Public Works this past February gave a green light to a second phase of the project in East Rockaway in Bay Park. That portion, the company said, was worth about $12 million.

AbTech describes itself as "a full-service environmental technologies and engineering firm dedicated to providing innovative solutions to communities, industry and governments addressing issues of water pollution and contamination."

News of the probe surfaces weeks after another one of the state's long-standing political figures in Albany, Assembly Speaker Sheldon Silver (D-Manhattan), was arrested by federal investigators on corruption charges.

With Zachary R. Dowdy

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and John Riley