WASHINGTON — Paul Whelan was in Moscow that day at the storied Metropole Hotel, getting ready for the wedding of a fellow U.S. Marine, when a longtime Russian friend, a junior officer in the frontier guards, dropped by unexpectedly.

The friend handed him a thumb drive that he said contained souvenir photos and videos from a trip the two men took around Russia months earlier. Whelan pocketed the drive, when a few men in civilian clothes, some with their faces covered by balaclavas, burst into the room.

“We are with the Federal Security Service, and you are under arrest for espionage,” Whelan recalled one of them saying in English.

Speaking in Washington in his first lengthy newspaper interview since he was released Aug. 1 in the largest East-West prisoner swap since the Cold War, Whelan, 54, said he thought the arrest, in late December 2018, was a prank.

It wasn’t.

Within hours, he found himself locked into a cell in Moscow’s notorious, high-security Lefortovo Prison, where Soviet-era political prisoners had been tortured. So began Whelan’s odyssey through what he described as Russia’s harsh, often surreal, state-manipulated criminal justice system. His ordeal lasted, by his own count, five years, seven months and five days.

At Lefortovo, he survived an emergency hernia surgery at night at a hospital where, he said, half the overhead lights did not work, and when the doctors dropped instruments on the floor, they picked them up and kept going. Sent to a labor camp after his conviction, he endured a diet of bread, tea and a watery fish soup that seemed better suited as cat food, as well as once-a-week cold showers and long days sewing buttons and buttonholes on winter uniforms for government workers.

“It was tedious, monotonous and filthy,” he said, adding: “You are somewhere you don’t necessarily want to be, you know, in miserable conditions, doing things you don’t want to do with people you don’t really want to be with. You have absolutely no control over when you’re going to leave and go home.”

Whelan’s arrest was a new chapter in what is called hostage diplomacy, when citizens of the United States or other nations are arrested and imprisoned on sham charges in order to be exchanged for a person or some concession.

The officers of the Federal Security Service, formerly the KGB, who took him were clear about their motive: to get three Russian prisoners held in the United States released.

“They said, ‘Well, you know, we’re hoping that the American government and our government will do a change, you for them,’ ” Whelan said, a statement that he said was repeated numerous times over the years.

Whelan first traveled to Russia in 2006 for pleasure while serving with the Marines in Iraq. A World War II buff, he was drawn to its major battlefields, and eventually visited at least six times. When arrested, he was the head of security for BorgWarner, a Michigan-based international auto parts manufacturer.

Along the way, he opened an account on VKontakte, Russia’s Facebook, and befriended about 70 Russians, usually men younger than himself, many with security backgrounds. Whelan, a former Michigan police officer, said he was hoping to trade insignia.

In 2008, Whelan received a “bad-conduct discharge” from the Marines, found guilty of trying to steal more than $10,000 in U.S. government funds in Iraq. He said he would only discuss the case in a planned memoir.

American officials have long pointed out that the United States, like most nations, dispatches spies with diplomatic passports — meaning they are immune from prosecution if accused, but usually expelled — and it would avoid sending anyone with a criminal record.

Whelan had known the officer who handed him the flash drive for 10 years: His own parents stayed at the Russian’s home near Moscow in 2009.

Russia, accusing Whelan of being a brigadier general in the U.S. Defense Intelligence Agency, insisted that he face a secret trial on espionage charges. The closed proceedings were “a sham,” Whelan said, a “Moscow goat rodeo,” designed to resemble a judicial process.

“They don’t want it to look like they’re just grabbing tourists out of hotels and charging them with espionage so they can hold them for ransom, which is what they’re doing,” he said.

The case hinged on the contents of the flash drive, which were never shown in court but prosecutors said included the names and photos of cadets at a department of the FSB. The drive was taken from him right after his arrest and never appeared again, Whelan said, with its contents retroactively declared classified.

During one session, the judge indicated that five cardboard boxes arrayed in front of him all contained evidence, none of which he or his FSB-appointed lawyers were allowed to read.

In June 2020, Whelan was sentenced to 16 years in a labor colony, and within minutes was told that he would be home within two weeks.

It proved to be far longer.

Initially it was thought that he was taken to trade for Maria Butina, accused in 2018 of acting as an unregistered Russian agent in the United States. But her relatively short prison sentence ended before Whelan was convicted.

In 2022, the U.S. government exchanged Viktor Bout, a Russian arms dealer, for basketball star Brittney Griner; and a drug trafficker, Konstantin Yaroshenko, for Trevor Reed, another former U.S. Marine.

Russia balked at including Whelan in either exchange.

“It was devastating,” Whelan said, feeling abandoned by the U.S. government. “I was obviously not as important as others.”

After his conviction he was sent from Lefortovo to the labor camp IK-17 in the remote region of Mordavia, southeast of Moscow.

In exchange for cigarettes, the guards would bring prisoners meat, fruit and dairy products to add to the meager prison diet. He could buy burner cellphones that way too, keeping in regular touch with his family.

Griner and her basketball teammates donated money to his prison account.

He was released in a historic exchange of 16 journalists, Russian opposition figures and others for eight Russians, including a convicted assassin.

While incarcerated, he lost his job and his apartment. Unmarried, he is back living with his elderly parents in Michigan, lacking the financial means to establish a new life. He has started a GoFundMe campaign.

He is doing advocacy work, he said, to get better medical care for his Central Asian friends still imprisoned in Russia, and to press for the release of incarcerated Americans.

“I can’t get revenge, right?” he said. “The only thing I can do is to look forward.”