Boris Nemtsov's name has been added to the list of Kremlin opponents who have been killed or died in suspicious circumstances in recent years.
Here are some of the key people to have died:
27 February, 2015: Leading opposition figure and former deputy prime minister Boris Nemtsov, 55, is shot dead just metres from the Kremlin, in the very heart of the Russian capital.
23 March, 2013: Former oligarch and fierce foe of Russian President Vladimir Putin, Boris Berezovsky, 67, is found hanged in a bathroom at his country home in the UK, where he was living in exile. Coroners record an open verdict into his death after being unable to confirm it was suicide despite strong evidence that Berezovsky had killed himself.
16 November, 2009: Financial lawyer Sergei Magnitsky, 37, dies after being denied medical treatment in a Moscow jail after denouncing official corruption. His death sparks a crisis between the United States and Russia after Washington passes the so-called "Magnitsky Act" to target Russian officials implicated in his demise.
15 July, 2009: Human rights activist Natalia Estemirova, 50, investigating government abuses in the volatile North Caucasus region of Chechnya is kidnapped in the local capital Grozny and found dead several hours later.
19 January, 2009: Human rights lawyer Stanislav Markelov, 34, and opposition journalist Anastasia Baburova, 25, are shot dead in the middle of a Moscow street after leaving a press conference.
23 November, 2006: Former intelligence officer turned Vladimir Putin critic Alexander Litvinenko, 43, dies after allegedly drinking tea laced with radioactive isotope polonium in a hotel in London, where he is living in exile. Two Russian businessmen and ex-KGB agents Dmitry Kovtun and Andrei Lugovoi are accused of poisoning Litvinenko by British authorities but Russia refuses to extradite them.
7 October, 2006: Journalist Anna Politkovskaya, 48, is shot dead at the entrance to her apartment block in central Moscow. Five men are eventually found guilty of carrying out the hit but those who ordered the murder have never been identified.
9 July, 2004: Investigative US journalist Paul Klebnikov, 41, dies after being shot as he leaves the offices of Forbes Russian-language version in Moscow. Klebnikov had angered oligarch Boris Berezovsky with his reporting and also probed the war in Chechnya. Over ten years since his murder no one has yet been found guilty.
17 April, 2003: Liberal politician Sergei Yushenkov, 52, is killed by a hitman as he returns to his home in Moscow. Yushenkov had probed a spate of devastating apartment bombings in 1999, which provided the pretext for the second Chechen War that helped propel Vladimir Putin to power.
