In 1998 Alexander Litvinenko — then an agent of the Federal Security Service (FSB) — and four other masked FSB agents held a press conference to say that they had been ordered to carry out assassinations. Litvinenko was fired by Vladimir Putin, then head of the FSB, and fled to Britain. He died after the radioactive chemical polonium-210 was slipped into his tea in 2006.

Mikhail Trepashkin, a former FSB agent, appeared at the same press conference to say that he had been a target of the assassination plot. He became a lawyer and part of an independent commission investigating bombings in Moscow apartment blocks in 1999. He claimed that the FSB was involved in the attacks. Mr Trepashkin was arrested in 2003, a week before he was due to represent a victim’s family in court, and was jailed for illegal arms possession. He was freed in 2007.

Mikhail Khodorkovsky became one of the richest men in Russia during the Yeltsin era and acquired a controlling stake in the Yukos Oil Company. He became a critic of Mr Putin after he came to power in 2000, complaining of corruption, a lack of democratic reform and providing funds for opposition groups. In 2003 he was sentenced to eight years in jail for fraud and tax evasion. He faces more charges of embezzlement and money laundering. Yukos went bankrupt in 2006.

Aleksandr Nikitin, a former Soviet engineer on nuclear submarines and a nuclear inspector, began publishing reports in 1994 saying that the Russians had illegally contaminated the ocean with nuclear waste. He was charged with treason and espionage but the charges were rejected by post-Soviet courts and he continues environmental campaigning.

The chemist Vil Mirzayanov published articles in 1991 about Russia’s development of the Novichok chemical weapon in contravention of an agreement with the US. He was arrested for revealing state secrets but released because of a lack of evidence. He now lives in the US.

Source: Times database

Times Recommends

• A life online: God likes a laugh
• How the Saints won the hearts of the nation
• Sri Lanka opposition leader held for 'coup'