Russian journalist Anna Politkovskaya (photo, from bbcimg.co.uk) was killed in 2006 and Rustam Makhmudov, the man suspected of shooting her, has been arrested in Chechnya.
Mr Makhmudov’s lawyer told AFP news agency that he was arrested overnight at his parents’ home.
He will be brought to Moscow.
Mr Makhmudov’s brothers Dzhabrail and Ibragim, along with former policeman Sergei Khadzhikurbanov, were charged with being involved in the murder, but not with ordering or carrying it.
They were all acquitted in a jury trial in 2009 on a lack of evidence, but Russia’s supreme court annulled the verdict and ordered them to be retried. They are currently awaiting trial over the murder in the Russian capital.
Anna Politkovskaya, 48, was an investigative journalist who was renowned for her opposition to the Chechen conflict, but she also reported on the alleged human rights abuses by Chechen rebels military forces under the leadership of Vladimir Putin, former Russian president and current prime minister.
In several of her books she talked about the Chechen wars and of Putin’s Russia, accusing Russian secret services of repressing civil liberties in order to re-establish a dictatorship based on the Soviet past. She received many prestigious international awards for her work.
She was shot dead in the stairwell of her apartment in Moscow on October 7 2006.
Ms Politkovskaya’s murder in cold blood caused shock and revulsion. It also sparked a strong international reaction because it was largely seen as a contract killing.
The announcement of Mr Makhmudov’s arrest was welcomed by Novaya Gazeta, a low-circulation Russian opposition newspaper where Ms Politkovskaya worked at the time of her death.
However a lawyer for the journalist’s family denied the arrest being a major breakthrough as investigators still had not established who ordered the assassination.
According to Dmitry Babich, a political analyst and journalist for the Russian International News Agency, or RIA Novosti, Politkovskaya’s colleagues at Novaya Gazeta believe that Mr Makhmudov is likely guilty of her killing.
He told Al Jazeera : “So the biggest question is not who performed the murder, but who ordered it.”
“You know that Novaya Gazeta is very much in opposition to the Russian government, so they suspect someone from the current leadership of Chechnya (which is pro-Moscow) is behind the assassination.
“The relatives of Politkovskaya and other fellow journalists agree that these two brothers were tracking her movements on the day she was killed. They were suspected of actually giving the signal to the killer who was waiting inside her (apartment) building.”
Russian television has broadcast a grainy CCTV footage from her building on which a man in a baseball cap can be seen following her inside just before the shooting.