Russian rebels pay with their lives

Alexander Litvinenko.

Boris Nemtsov is not the first Russian dissident to die in mysterious circumstances in recent years:

Paul Khlebnikov, 2004
An American journalist and editor of Forbes Russia, he was shot outside his Moscow office. Khlebnikov, 41 was known for his investigations into corruption and Russian business and politics. Three men from Chechnya were acquitted of his murder in 2006. The case has never been solved.

Anna Politkovskaya, 2006
A journalist and fierce Kremlin critic, she was shot in the entrance to her apartment building in Moscow, aged 48. She was known for her reporting on human rights abuses in the North Caucasus. Supporters maintain that the murder was political. Five men were found guilty last year of carrying out the shooting, but the person who ordered the killing has never been identified.

Anna Politkovskaya.

Alexander Litvinenko, 2006
The 44-year-old former KGB officer died after being poisoned with radioactive polonium-210. Two former Russian security service men allegedly added the poison to his tea at a London hotel. Litvinenko had accused Vladimir Putin of corruption.

Natalya Estemirova, 2009
Abducted in the Chechen capital of Grozny in July 2009, Natalya Estemirova, a 50-year-old human rights campaigner and activist, was later found dumped with bullet wounds to her head. The case intensified scrutiny of local leader Ramzan Kadyrov, who was accused of creating a climate of fear and violence. Estemirova's killers have never been brought to justice.

Anastasiya Baburova and Stanislav Markelov, 2009
Baburova, a trainee journalist, and Markelov, a human rights lawyer, were shot in broad daylight 2km from the Kremlin. The main target was assumed to be Markelov, 34 at the time, who had represented left-wing activists, journalists and victims of the 2002 Moscow theatre siege. In 2011 a court convicted two neo-nazis for the double murder.