A Moscow court on Sunday charged two men with alleged involvement in the murder of opposition politician Boris Nemtsov and confirmed the arrest of three other suspects.
Zaur Dadayev, deputy commander of the "North" Battalion, a unit of the Chechen security services under the patronage of the Caucasus republic's leader Ramzan Kadyrov, had admitted his involvement in the crime, said Judge Natalia Mushnikova.
Anzor Gubashev, a cousin of Mr Dadayev, was also indicted but said he was not guilty.
The court said Mr Dadayev was to remain in custody until at least April 28. It also extended the detention of Mr Gubashev's brother Shagit Gubashev, Khamzat Bakhayev and Tamerlan Eskerkhanov until early May. All three men said they were innocent.
Nemtsov, 55, was killed with several shots in the back and the head shortly before midnight on February 27 on a bridge just outside the Kremlin walls, according to the Federal Investigation Committee, Russia's top investigative unit which directly reports to president Vladimir Putin.
Mr Kadyrov late on Sunday appeared to throw his weight behind Mr Dadayev, calling him a "true patriot".
Mr Dadayev had been "one of the most fearless and courageous soldiers of the regiment," Mr Kadyrov wrote on his Instagram account. "If the court confirms his guilt, then, having killed a man, he committed a serious crime. But I want to mention again that he could not take one step against Russia, for whom he risked his own life for many years."
The Chechen leader said he had asked his security council to look into why Mr Dadayev had been let go from the interior ministry's troops.
Mr Kadyrov also appeared to suggest that the Nemtsov murder could have been related to the opposition leader's criticism of the terrorist attack against Charlie Hebdo, the cartoon magazine, in Paris in January. "Anyone who knows Zaur will confirm that he is a deeply religious man and that he, like all Muslims, was shocked by the actions of Charlie [Hebdo] and comments in support of printing the cartoons," he wrote.
Immediately after the murder last week, the Federal Investigation Committee had named a potential link to Islamist terrorism as one direction of its probe.
In January, Nemtsov had criticised the attack against Charlie Hebdo, however without expressing support for the cartoons mocking Islam. He argued in a blog post that the attack was an example of "medieval" Islamic inquisition which people needed to stand up to. "Centuries will pass and Islam will grow up, and terrorism will be a thing of the past," he wrote. "But to sit and do nothing is not an option."
The rapid presentation of five suspects, all apparently from the restive North Caucasus region, and an alleged confession stirred a new wave of debate among government critics.
Some observers said the arrests were in line with the pattern of earlier political murders in Russia where men from Chechnya and other North Caucasus republics were found guilty of murder but the identity of those who had ordered the killings remained unknown.
"It is extremely important that the case is not limited to catching the shooters — whether they are the real killers or not," Ilya Yashin, a friend and political associate of Nemtsov's, wrote on his blog. "The key task is establishing and arresting those who gave the order."
The investigative committee said Mr Dadayev and Anzor Gubashev were accused of helping organise and executing the killing of Mr Nemtsov. Neither the investigators nor the procurator gave further details on how the defendants or the other suspects were alleged to have been involved in the crime.
Other observers noted that it was surprising the authorities had come up with an entire group of suspects after initially struggling to even find the getaway car.
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At the weekend, Russian media quoted investigators as saying that Mr Dadayev and Anzor Gubashev had been identified with the help of testimony from members of the security services who had witnessed the murder.
Earlier, it had been assumed that Anna Duritskaya, Nemtsov's Ukrainian girlfriend who according to the investigation was walking arm-in-arm with him when he was shot, was the only witness.
But this notion has been contested by many members of the opposition. Alexei Navalny, the anti-corruption blogger, has said it had to be assumed that Nemtsov, as a leading politician, was under constant surveillance from security officials, suggesting that the murder could only have happened with backing from the political leadership.
Zhanna Nemtsova, the murdered politician's daughter, has also pointed the finger at Mr Putin with the same argument.
Footage from a security camera on the other side of the bridge which Russian television stations said showed the moment of the murder appeared to reveal several people arriving on foot at the scene shortly after the murder.