David B. Massey, a federal prosecutor who played a significant role in government’s sweeping investigation into insider trading in the hedge fund industry, is joining the white-collar defense firm Richards Kibbe & Orbe. He becomes the latest government lawyer to move into private practice.

During his nine years as an assistant federal prosecutor in New York, Mr. Massey led the prosecution of the Swiss bank Wegelin & Company, which was indicted in February 2012 on charges of helping United States citizens hide more than $1.2 billion from the Internal Revenue Service. The private bank pleaded guilty this year to a tax evasion conspiracy charge and paid $74 million and fines and restitution.

Mr. Massey was also involved also the prosecution of the former hedge fund manager Joseph Skowron on insider trading charges. Another case involved John Kinnucan, a onetime independent research consultant who had taunted F.B.I. agents and prosecutors looking into insider trading. Mr. Kinnucan ultimately pleaded guilty and was sentenced to more than four years in prison for providing inside tips to a number of traders and analysts working at hedge funds and mutual funds.

Over the last several years, a number of prosecutors who played critical roles in the insider trading investigation have moved to private practice, including Reed Brodsky, who went to Gibson, Dunn & Crutcher; Andrew Z. Michaelson, who joined Boies Schiller & Flexner; and Jonathan R. Streeter, now at Dechert.

A graduate of Yale Law School in 1997, Mr. Massey joined the United States attorney’s office for the Southern District of New York in 2004, after a brief stint as a litigation associate at the law firm Davis, Polk & Wardwell. Mr. Massey said in an interview that he began thinking of returning to the private sector earlier this year. He said timing of his move worked out because he had just “wrapped up a number of things” he had worked on for several years.

One of those matters was the successful prosecution of Tyrone L. Gilliams Jr., a former Philadelphia commodities trader and hip-hop promoter convicted by a federal jury of bilking investors out of at least $5 million. In October, Mr. Gilliams, who had been a former star basketball player for the University of Pennsylvania, was sentenced to 10 years in jail.