Why were Evan Gershkovich, Paul Whelan and others being held prisoner in Russia?

Here's a look at the Americans and permanent U.S. resident freed as part of the 24-prisoner exchange with Russia happening Thursday -- the largest of its kind since the Cold War -- as announced by President Joe Biden.

Evan Gershkovich

The 32-year-old Wall Street Journal reporter was sentenced last month to 16 years in a Russian penal colony on charges of espionage after a guilty verdict was announced in his closed-door trial. His newspaper and the U.S. had denounced the legal proceedings, which saw only two days of hearings, as a sham and have denied the allegations. The American was arrested in March 2023 while on a reporting trip in Yekaterinburg, with the U.S. classifying him as unjustly detained.

Paul Whelan

The 54-year-old former U.S. Marine was sentenced to 16 years in a Russian prison following a closed-door trial in June 2020. He was convicted of spying charges, which he and the U.S. have claimed were fabricated in order to seize him as a political hostage. The U.S. classified him as wrongfully detained following his arrest in 2018 while visiting Moscow for a friend's wedding. In his first interview following his conviction, Whelan, who worked for the auto parts supplier BorgWarner at the time of his arrest, told ABC News he believed he was targeted partly due to sanctions retaliation.

Alsu Kurmasheva

The U.S.-Russian journalist for Radio Free Europe/Radio Liberty was sentenced to 6 ½ years in a Russian penal colony last month after being convicted of spreading false information about the Russian army following a secret trial, The Associated Press reported. After traveling to Russia for a family emergency, she was initially detained at an airport in June 2023 while returning home to Prague, her news outlet said. The 47-year-old mother of two was initially fined for failing to register her U.S. passport with Russian authorities before being charged months later in what U.S. officials said appeared to be a case of Russia harassing U.S. citizens.

Vladimir Kara-Murza

One of Russia's most high-profile Kremlin critics, who has survived two poisonings, the dual British and Russian citizen was sentenced to 25 years in prison in April 2023 on charges of treason for criticizing the war in Ukraine in what was widely viewed as a show trial. Kara-Murza, 42, is a U.S. lawful permanent resident, with his wife and children living in the U.S., and a contributing opinion writer for The Washington Post who was awarded the 2024 Pulitzer Prize for commentary while imprisoned. Concerns about his health had been mounting after he was recently moved to a prison hospital and his lawyers said they were being denied access to him, as well as following the death of Russia's best-known opposition leader Alexei Navalny in prison in February.

This is a developing story. Please check back for updates.