Reza Zarrab was a well-connected Turkish-Iranian gold trader known for throwing money around with abandon, paying tens of millions of dollars in bribes to Turkish officials.

When he was arrested in 2016 and jailed at the Metropolitan Correctional Center, an ultrasecure federal lockup in Manhattan, one of the guards, Victor Casado, 36, of the Bronx, saw an opportunity and offered his services.

Over a year, he smuggling in alcohol, cellphones and vitamin C packets, among other things, for Mr. Zarrab in exchange for at least $50,000 in bribes, the authorities said.

Mr. Casado was eventually arrested and pleaded guilty to federal bribery charges last summer. On Friday, Mr. Casado, a former New York City police officer who was forced to resign after he committed perjury in court, stood before a federal judge and was sentenced to three years in prison and three years supervised release.