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.