By Jonathan Stempel

NEW YORK (Reuters) -U.S. prosecutors on Thursday announced criminal insider trading charges against a former Goldman Sachs and Blackstone analyst and two friends over an alleged scheme to trade on nonpublic information about planned mergers and strategic partnerships.

Authorities said former analyst Anthony Viggiano, 26, of Baldwin, New York, passed tips on at least eight transactions between 2021 and 2023 to Christopher Salamone, 35, a construction sales representative he has known for two decades and who grew up on the same block.

Viggiano also allegedly tipped his college friend Stephen Forlano, 27, who tipped others including his college friend Nathan Bleckley, 26, a U.S. Army captain.

Subsequent trades generated more than $580,000 of illegal profit, including $322,000 for Salamone, according to court papers.

The Department of Justice said that Salamone, of Long Beach, New York, pleaded guilty to three counts of securities fraud and one count of conspiracy, and is cooperating with its probe.

Viggiano faces nine securities fraud and conspiracy charges, while Forlano, of Tampa, Florida, faces four.

All four men also face related civil charges from the Securities and Exchange Commission. Bleckley lives in Altus, Oklahoma.

The eight transactions included American International Group's sale of part of its life and retirement unit to Blackstone, and private equity firm Advent International's agreement to buy satellite operator Maxar Technologies for about $6.4 billion including debt. Goldman advised Advent.

According to the SEC, Viggiano and Salamone invested in four other defense companies as a "smokescreen" when they bought Maxar securities, so they could say they were buying defense stocks "in anticipation of a possible World War III."

Viggiano "betrayed the trust of his employers," U.S. Attorney Damian Williams in Manhattan said in a statement.

Steven Brill, a lawyer for Viggiano, declined to comment.

Forlano's lawyer Michael Bachner said his client denied wrongdoing and would contest the charges vigorously.

Bleckley's lawyer Todd Spodek said his client, "a dedicated member of the armed forces, places a high priority on doing what's right. We eagerly anticipate closing this chapter of his life."

Salamone's lawyer was not immediately available for comment.

Viggiano worked at Blackstone for about seven months, and at Goldman for more than a year before terminating him.

In separate statements, Blackstone and Goldman said they were cooperating with authorities and had "zero tolerance" for the alleged misconduct, saying it violated their business standards. Blackstone added that Viggiano had a "non-investment" role at the firm.

(Reporting by Jonathan Stempel in New York; editing by Rami Ayyub and Leslie Adler)