A veteran liberal member of Russia's State Duma, or parliament, has been shot dead in a Moscow suburb.
Police say Yushenkov was shot with a silenced weapon
Sergey Yushenkov was shot several times in the chest in the latest political assassination to rock post-Soviet Russia.
The BBC's Russian affairs analyst Stephen Dalziel says such a high-profile killing stands out even in a country where murders of politicians and businessmen are relatively common.
Police said the killer apparently used a gun with a silencer to shoot Yushenkov several times as he walked from his car to his apartment building. The gunman then fled the scene.
Mr Yushenkov was one of the co-founders of a new political party, Liberal Russia.
Another MP from the party, Vladimir Golovlev, was shot dead last August in a killing which Mr Yushenkov described as politically motivated.
The party was at one stage in funding talks with Boris Berezovsky, the exiled Russian tycoon now facing extradition from the UK on fraud charges, but negotiations broke down.
Mr Yushenkov, a former colonel in the Soviet army, was no stranger to controversy.
He was a strong proponent of military reform and favoured the creation of a free market in Russia when many deputies were dragging their feet.
In 2000, he was involved in setting up the Liberal Russia Party which finally achieved full legal registration just hours before he was shot near his home in north-west Moscow.
The BBC's Stephen Dalziel in Moscow, says many Russians will regard the murder of one of the country's leading liberals as a serious threat to the democratic process, with parliamentary elections due in December.
He says Mr Yushenkov was admired by many for his high political principles and his honesty.
He was not afraid to criticise the Russian political establishment, including President Vladimir Putin and spoke out against human rights abuses and the war in Chechnya.
But in his message of condolences on Thursday, Mr Putin paid tribute to an "outstanding politician of our time... who considered it his obligation to defend democratic freedoms and ideals".