The accusations also raised questions about what agency secrets Mr. McGonigal might have compromised. But a more than three-year F.B.I. investigation produced no evidence that he had done so, according to U.S. officials who spoke on condition of anonymity to discuss the sensitive matter. That a plea agreement may be reached relatively quickly also suggests that Mr. McGonigal’s former colleagues at the F.B.I., and Justice Department prosecutors, have concluded his behavior stopped at corruption and did not extend to espionage.

The New York indictment accused Mr. McGonigal and Mr. Shestakov of working for Mr. Deripaska, a wealthy Russian metals magnate. Mr. Shestakov, 69, is a former Soviet and Russian diplomat who lived in the U.S. and worked after his retirement as an interpreter in U.S. courts in New York.

Federal prosecutors suggested that while still at the F.B.I., Mr. McGonigal attempted to build a relationship with an aide to Mr. Deripaska by arranging for the aide’s daughter to do an internship with the New York City Police Department. (A senior police official told The New York Times that the woman was given a “V.I.P.-type” tour over several days that included spending time with specialized Police Department units, including the harbor patrol and mounted units, but it was not an internship.)

In April 2018, Mr. Deripaska was placed on a sanctions list by the U.S. State Department, which cited his connections to the Kremlin and Russia’s interference in the presidential election of 2016. Mr. McGonigal reviewed the proposed list of people to be sanctioned, including Mr. Deripaska, before it was finalized, prosecutors said.

In 2019, after Mr. McGonigal’s retirement, he and Mr. Shestakov connected Mr. Deripaska to a law firm for aid in getting the sanctions lifted, federal prosecutors in New York said. Mr. McGonigal met with Mr. Deripaska and others in London and Vienna and was paid $25,000 a month through the law firm as a consultant and an investigator until about March 2020, the indictment says.

Then, in the spring of 2021, Mr. McGonigal and Mr. Shestakov negotiated an agreement with Mr. Deripaska’s aide to investigate a rival oligarch, for which they were paid more than $200,000, according to the indictment. The criminal charges in the indictment appear to relate primarily to this arrangement, which ended, prosecutors said, when the men’s devices were seized by the F.B.I. in November 2021.

Adam Goldman and William K. Rashbaum contributed reporting. Susan C. Beachy contributed research.