WASHINGTON (AP) - A Justice Department prosecutor killed himself while under investigation over whether he and other attorneys in the prosecution of Sen. Ted Stevens acted improperly in the case, officials said.

Nicholas Marsh, 37, committed suicide on Sunday, two years after being part of the Justice Department team that convicted Stevens on corruption charges that were eventually thrown out. Marsh's suicide was confirmed by his lawyer, Robert Luskin.

"I think Nick loved being a prosecutor and I think he was incredibly fearful that this would prevent him from continuing to work for the Justice Department," Luskin said Monday. "It's incredibly tragic after all this time when we were on the verge of a successful resolution."

The prosecutors in the Stevens case failed to disclose evidence favorable to the defendant as Supreme Court precedent requires. The omission was so serious that Attorney General Eric Holder stepped in and asked a federal judge to throw out Stevens' convictions, which the judge did, while taking the additional step of appointing prominent Washington attorney Henry Schuelke to investigate possible improprieties by the prosecutors.

"My general sense is that with the direction things are going, I really would have been shocked if Hank had done anything other than exonerate Nick Marsh," said Luskin, who called the suicide a "terrible tragedy."

He said his impression was that the investigation was drawing to a close.

"I think we were within shouting distance of the finish line," the attorney said.

Stevens, a longtime Republican senator from Alaska, lost his Senate seat in an election shortly after his October 2008 conviction. He died in a plane crash in Alaska in August.

Lanny Breuer, the assistant attorney general in charge of the Justice Department's criminal division, said, "Our deepest sympathies go out to Nick's family and friends on this sad day. The Department of Justice is a community, and today our community is mourning the loss of this dedicated young attorney."

During the Schuelke investigation, Marsh had been transferred from the department's Public Integrity Section, which handles corruption probes. He most recently had been working in the department's Office of International Affairs.

"Notwithstanding the unfounded accusations recently made against him, he took his ethical and professional obligations as seriously as any prosecutor or lawyer I've ever met," Joshua Berman, a former prosecutor and close friend of Marsh, said in a statement.