The release of Brittney Griner, the American basketball star imprisoned in Russia who was exchanged Thursday for Russian arms dealer Viktor Bout, raised questions about the case of another American prisoner, Paul Whelan.

U.S. officials say they are still working to secure the release of the former Marine, who was arrested in Moscow in 2019, but claim he was not part of the negotiations for Thursday’s prisoner swap.

Who is Paul Whelan?

Paul Whelan, 52, is a Marine turned corporate security executive who was convicted of espionage and is serving a 16-year sentence in a Russian prison.

He is a citizen of four countries - the United States, Canada, Britain and Ireland. He received a bad-conduct discharge from the Marines in 2008, according to military records. He later became the corporate security director at BorgWarner, a Michigan-based automotive parts supplier.

Why is Whelan in Russia?

In June 2020, Whelan was sentenced to 16 years of hard labor in a Russian prison for espionage, in a trial that he has argued was politically motivated and heightened tensions between the United States and Russia.

His attorney, Vladimir Zherebenkov, has said his client unwittingly received a flash drive containing “state secrets” while visiting Russia for a wedding in 2018. Foreign Minister Sergei Lavrov said Whelan was caught “red-handed.”

Whelan, arrested Dec. 28, 2018, in a Moscow hotel, has said he thought the flash drive that he received from an acquaintance contained holiday photos. Whelan, his family and the U.S. government have repeatedly stated that the charges are baseless and that he was framed.

The day the verdict was announced, Whelan said he thought it was a foregone conclusion, and shouted from within a glass-enclosed area in the courtroom that Russia “feels impotent in the world, so they’re taking political hostages.”

How long has Whelan been held in a Russian penal colony?

Whelan has been detained in Russia for nearly four years, and in August 2020, he was sent to prison camp IK-17 in the Mordovia region of Russia, some 210 miles east of Moscow.

In an interview with ABC News in November 2020, Whelan described the place as "very, very old. It's very grim. Quite dilapidated." The former Marine said he was living in "quite crowded" spaces and estimated that his building housed 50 to 60 people. He described his fellow inmates as "quite welcoming."

During his imprisonment, Whelan has been working in a clothing factory, which he called a "sweatshop" in a 2021 interview with CNN. His mornings begin at 6 a.m. and his routine is monotonous, but writing letters and reading books in English helped him get through it, he said. He also told CNN he had a recurring cough and noted that getting medical care was difficult — even prevented by guards — in the colony.

Since entering Russian custody, Whelan has faced changing conditions. Last year, he was sent to solitary confinement for a month. Concern for Whelan flared up again in November after he was not able to contact his family for more than a week and Russian authorities claimed he had been sent to a hospital.

He got in touch with his parents Dec. 2., in what Whelan's brother described as a "proof of life" call, according to the Associated Press.

Why was he not released?

After news of Griner’s release Thursday, U.S. officials lamented not being able to secure Whelan’s release, but said they were continuing the efforts.

President Biden said Thursday that his administration has “not forgotten about Paul Whelan, who has been unjustly detained in Russia for years.”

“We’ll keep negotiating in good faith for Paul’s release. I guarantee that. I say that to the family,” Biden told reporters at the White House.

Meanwhile, Whelan said Thursday that he is “greatly disappointed” that the government has not done more to secure his release, “especially as the four-year anniversary of my arrest is coming up. I was arrested for a crime that never occurred,” he said in a phone interview with CNN from the remote Russian penal colony where he is being detained. “I don’t understand why I’m still sitting here.”

Following the announcement of Griner’s release, Russian lawyers for Whelan also lamented that their client was not included in the swap. Over the summer, reports indicated that the U.S. government was trying to negotiate the release of both Griner and Whelan in exchange for Bout.

“There was a lot of speculation about this and there was hope [that] Paul and his family had hoped he would finally return home to his very elderly parents,” his lawyer Olga Karlova told The Post.

“We don’t know exactly why [he hasn’t been added], maybe because he is too valuable for the swap, and they’ve decided to hold him for longer,” she added.

A national security official said Thursday that Whelan was never really an option for the Russians during the negotiations about freeing Griner, and that given the nature of the espionage charges against him, Russians treat Whelan “differently.”

“This is not a situation where we had a choice of which American to bring home. It was a choice of bringing home one American, Brittney Griner, or bringing home none,” the official said, speaking on the condition of anonymity on a call with reporters.

Officials have said the dialogue about Whelan’s release remains open.

This is the second time Whelan has been overlooked in a prisoner swap between Moscow and Washington. Earlier this year, American Trevor Reed, a former Marine who was detained in 2019, was exchanged for Konstantin Yaroshenko, a Russian pilot who was convicted of drug smuggling and sentenced to 20 years in a U.S. prison.

The Washington Post’s Cleve R. Wootson Jr. contributed to this report.