A former Yukos executive diagnosed with HIV several months after he was arrested died Monday of complications caused by AIDS, his family said.
The family of Vasily Alexanyan told Dojd television channel that he had died at his home in Moscow at age 39.
Harvard-educated Alexanyan, a vice president at Russia's largest oil company, was arrested in 2006 on embezzlement and money-laundering charges.
He also served as a lawyer for Yukos owner Mikhail Khodorkovsky following his 2003 arrest that was widely seen as Kremlin revenge against Khodorkovsky's political ambitions.
Khodorkovsky is still serving a 13-year sentence on embezzlement and money-laundering charges.
Following the diagnosis, Alexanyan contracted tuberculosis and went nearly blind before his release on bail in 2008.
Khodorkovsky, Western governments and politicians have described the Russian government's treatment of Alexanyan in prison and hospital as "inhumane."
Alexanyan's lawyers have said he was handcuffed to his bed while in the prison hospital, where his legal team and family were denied access to him.
Charges against Alexanyan were dropped in June 2010.
Yukos, once Russia's largest oil producer, was broken up and sold off in auctions ordered by the state to pay off billions of dollars in alleged back taxes,