The man suspected of shooting Russian journalist Anna Politkovskaya in 2006 has been arrested in Chechnya and is due to be brought to Moscow.
Rustam Makhmudov was arrested overnight at his parents' home, his lawyer told AFP news agency.
Two of the detainee's brothers and a third man are currently awaiting trial over the murder in Moscow.
Politkovskaya's murder in cold blood outside her home in the Russian capital caused shock and revulsion.
Rustam Makhmudov's brothers, Dzhabrail and Ibragim, have been accused of acting as drivers at the scene of the crime while former police officer Sergei Khadzhikurbanov has been accused of providing logistical support.
All three men were tried and acquitted for lack of evidence in 2009 but the verdict was overturned by Russia's supreme court, which ordered them to be retried.
Rustam Makhmudov remained a fugitive through his brothers' first trial.
Confirming the arrest, Russian prosecutors said the detainee would be transferred to Moscow "shortly" as part of the investigatory procedure.
Mr Makhmudov's lawyer, Saidakhmet Arsamerzayev, said the defence would seek to disprove key video evidence which allegedly shows his client's face.
"I have always said that investigators don't really need to arrest Rustam because his arrest will not confirm that he is the killer," Mr Arsamerzayev added.
"Right now it is clear that Rustam was not difficult to capture. He was hiding of course, but even so, he was taken at his house."
The suspect, 37, was born in Achkoi-Martan, Chechnya, according to his profile on Interpol's website.
Politkovskaya was a human rights campaigner and Russia's most famous investigative journalist, the BBC's Steve Rosenberg reports from Moscow.
Her reports were often highly critical not only of the Kremlin, but of the actions of the Russian military in Chechnya and of the pro-Moscow Chechen authorities, he notes.
A lawyer for Politkovskaya's family denied the arrest was a major breakthrough since investigators had yet to establish who it was that ordered the assassination.
At the time of her death, aged 48, the journalist was working for a low-circulation Russian newspaper, Novaya Gazeta, known for its fierce attacks on the country's authorities.
On 7 October 2006, she was found shot dead in a lift at her apartment block with a pistol and four bullets lying near her body.
Grainy CCTV footage from the building, which was broadcast on Russian television, showed a man in a baseball cap following her inside just before the shooting.
The arrest was welcomed by Novaya Gazeta.
"We hope that the jury can see for themselves that the prosecution was right," editor-in-chief Dmitry Muratov was quoted as saying by AFP.