Khalid Mehdiyev returned a phone call in the summer of 2022 from a fellow member of the Russian mob, Polad Omarov. They had been collaborating on a project, Mr. Mehdiyev said, extorting a grocery store owner in Brooklyn.

Now, Mr. Omarov said, he had been offered a bigger job by some people he knew.

“They want the journalist die,” Mr. Mehdiyev said Mr. Omarov told him. “They want to give that job to us.”

Over several days in a Manhattan murder-for-hire trial, Mr. Mehdiyev, an Azerbaijani member of a Russian crime syndicate, gave a detailed description of how Mr. Omarov had directed him in a failed plot to murder Masih Alinejad, an Iranian-born journalist and dissident living in Brooklyn.

Mr. Mehdiyev, 27, a bearded, burly man who wore dark-green prison garb in court, spoke in a flat voice with occasionally mixed-up grammar or pronunciation as he delivered his account of the realities of transnational repression — fancy words for the blunt threat of violence.

He described coercing business owners for a group of mobsters called the Thieves-in-Law while living in Yonkers, N.Y. A restaurant was burned and a Range Rover was filled with bullet holes. Meetings with enforcers named Man Man and Sonny took place in a Bronx pizzeria where a woman behind the counter would help Mr. Mehdiyev pick up money from the mob.

Mr. Omarov and a second mobster, Rafat Amirov, both accused of murder for hire and conspiracy, have been on trial in Federal District Court since Monday. Mr. Mehdiyev, who was arrested in 2022 near Ms. Alinejad’s home with an AK-47-style assault rifle, had faced the same charges. But he took the stand as a government witness, saying he had pleaded guilty to several offenses including attempted murder and possession of an illegal firearm.