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The United States government completed a prisoner exchange with Russia on Thursday after months of negotiations that resulted in the release of Russian arms dealer Viktor Bout for American women's basketball athlete Brittney Griner but left behind former U.S. Marine Paul Whelan.

Initially, the Biden administration had sought to release both Griner and Whelan for the notorious "Merchant of Death," who has served 11 years of a 25-year conviction, but the Kremlin gave the U.S. the option of only Griner's return or no deal at all. The female athlete was arrested in Russia in February 2022 after airport officials discovered cannabis oil contained in her vape cartridges.

The grounds for Whelan's arrest remain dubious, with different accounts from U.S. and Russian authorities. Whelan has been in Russian custody for nearly four years, convicted on charges of espionage and spying for the U.S. government and sentenced to 16 years in prison. Whelan and the U.S. have denied the charges as the 52-year-old remains imprisoned at a labor camp in Russia's Mordovia republic.

Whelan's family congratulated Griner for gaining her freedom but criticized the Biden administration for leaving Whelan behind for the second time during a prisoner exchange.

WHO IS VIKTOR BOUT, RUSSIA'S 'MERCHANT OF DEATH' FREED IN PRISONER SWAP FOR BRITTNEY GRINER?

Paul Whelan in court

Paul Whelan, a former U.S. Marine who was arrested for alleged spying, was convicted in a Russian court on June 15, 2020. (Sofia Sandurskaya, Moscow News Agency photo via AP)

"She will be reunited with her family. Brittney is free. And Paul is still a hostage. But how many more times do I need to write that?" David Whelan, Paul's brother, wrote in a statement on Thursday. "Despite the possibility that there might be an exchange without Paul, our family is still devastated. I can't even fathom how Paul will feel when he learns. Paul has worked so hard to survive nearly 4 years of this injustice."

On Dec. 28, 2018, while staying in a hotel in the Moscow area, Whelan was arrested by the Russian Federal Security Service. At the time, Whelan had reportedly arrived in the Russian capital to attend the wedding for a friend and act as a travel guide for the groom's family. However, Russian officials claimed that Whelan had met with an unnamed Russian citizen who gave the former Marine a USB drive containing classified material.

At the time, Whelan resided officially in Michigan, working as a corporate security executive for auto-parts manufacturer BorgWarner. Whelan had reportedly used his position to connect with law enforcement across different countries and had official citizenship outside the U.S. with Ireland and the United Kingdom. After serving in Iraq, he was dishonorably discharged from the Marine Corps for larceny and other poor conduct-related charges. 

Whelan's brother, David, said he was able to enter Russia using his U.S. passport and planned to leave the country on a flight from Saint Petersburg on Jan. 6, 2019. Russian news agencies also claimed Whelan had $80,000 in cash temporarily confiscated during an airport customs inspection.

Previously, Whelan had been left behind in another prisoner exchange that took place in April during the prisoner transfer for Russian citizen Konstantin Yaroshenko and imprisoned U.S. citizen Trevor Reed. The U.S. government at the time had reportedly not informed Whelan's family that he would not be included in the exchange.

The Bring Our Families Home Campaign, a group that advocates for U.S. citizens wrongfully detained in foreign countries, also criticized both the former and current presidential administrations for not securing Whelan's release in the last four years.

BIDEN PRISONER EXCHANGE FOR BRITTNEY GRINER LEAVES BEHIND MARINE VETERAN PAUL WHELAN — AGAIN

Joe Biden speaking

President Biden vowed to continue negotiations with the Russian government to return Paul Whelan back to the United States. (Chip Somodevilla/Getty Images)

"Paul Whelan has been let down and left behind at least three times by 2 Presidents," said the organization in a statement. "He deserves better from his government, and our Campaign implores President Biden to urgently secure Paul's immediate return using all tools available."

Vladimir Zherebenkov, Whelan's attorney based in Russia, expressed disappointment that Whelan was not included in the release but said choosing Griner was the "more humane" option because his client was in the military while the athlete was an Olympic champion. Zherebenkov also told the press that negotiations to free Whelan would continue and hopes another exchange could see his client freed in the next few months.

Meanwhile, President Joe Biden said Russia is treating negotiations over Whelan differently for "illegitimate reasons" and vowed to continue negotiations for his release, adding, "We have not forgotten about Paul Whelan."

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