October 25 marks 10 years since jailed former oil tycoon Mikhail Khodorkovsky was arrested by Russian authorities.
Khodorkovsky, once Russia's richest man, was eventually convicted of tax evasion and sentenced to eight years in prison.
In 2010, he was given a second prison term for money laundering and embezzlement from Yukos oil company, which he headed.
Khodorkovsky is set to be released in August, and his former business partner Platon Lebedev, who was arrested a few months earlier, is expected to be freed in May.
However, Khodorkovsky's supporters fear that new charges could be prepared to keep him behind the bars.
Critics call charges against Khodorkovsky punishment for having challenged President Vladimir Putin's dominance on Russia's political scene.
In a statement on October 25, the U.S. State Department reiterated its concerns about selective prosecution, a politically motivated investigation, and lack of respect for due process rights in Khodorkovsky's and Lebedev's cases.
PHOTOGALLERY: From Young Tycoon To Graying Inmate
Mikhail Khodorkovsky in 1992, when he was chairman of the board of directors of Menatep bank
Khodorkovsky with his family in October 1992
Khodorkovsky and his family at their dacha in 1992
Khodorkovsky, Russian Prime Minister Viktor Chernomyrdin (center), and Fuel and Energy Minister Sergei Kiriyenko (right) during the signing of a memorandum of intention to merge the Yukos and Sibneft companies on January 6, 1998
Khodorkovsky meets with Russian President Vladimir Putin in March 2002. Khodorkovsky challenged the Kremlin's authority by funding NGOs and opposition parties, lobbying to privatize the state-owned oil pipeline monopoly, and accusing Kremlin officials of corruption.
Khodorkovsky speaks at the Yukos headquarters in Moscow in June 2003, months before his arrest on fraud and tax evasion charges.
Russian police escort the former Yukos oil chief to a courthouse in Moscow on December 23, 2003.
Khodorkovsky supporters protest outside a Moscow court on January 15, 2004. Many Russians see him as a political prisoner jailed for political ambition and his criticism of President Putin. Amnesty International considers him a prisoner of conscience.
Khodorkovsky and Platon Lebedev hear the verdict in a Moscow court on May 16, 2005.
Khodorkovsky at a hearing at the Chita Regional Court in October 2008. During his imprisonment, Yukos was broken up and sold off, mostly into state hands.
Supporters rally on August 27, 2009, as prosecutors presented new charges against Khodorkovsky.
Khodorkovsky and Lebedev are escorted to a hearing in Moscow on January 11, 2010.
Elena Lukyanova (left), a lawyer for Khodorkovsky, and his daughter Anastasia Khodorkovskaya attend "Znamya" magazine's literary award ceremony in January 2010, where Khodorkovskaya received an award on her father's behalf for his "Dialogues With Lyudmila Ulitskaya."
The former CEO's mother, Marina Khodorkovskaya (right), his wife Inna (left), and his daughter Anastasia walk out after a court hearing in Moscow on December 30, 2010. A judge sentenced Khodorkovsky to additional prison time on new charges of financial crimes.
Khodorkovsky's book "Articles. Dialogues. Interviews." is presented in Moscow in January 2011.
Khodorkovsky and Lebedev stand in the defendants' box during a hearing in Moscow in May 2011.
Police detain a Khodorkovsky supporter during a gathering in central Moscow in June 2011.
Activists in London send a birthday message to Khodorkovsky in 2012. On June 26, 2013, he celebrated his 50th birthday in a remote prison colony near the Arctic Circle.
Members of a pro-Kremlin youth group wear masks representing anti-Putin opposition leaders during a demonstration called "Send them to join Khodorkovsky as guests!" on the occasion of the jailed businessman's 50th birthday.
Based on reporting by AP and ITAR-TASS