A Moscow court has charged two men in connection with the murder of Russian opposition activist Boris Nemtsov.
It said one of the men, Zaur Dadayev, had admitted involvement in the shooting on a bridge near the Kremlin on 27 February.
He and the other accused, Anzor Gubashev, are of Chechen origin.
Three other suspects were remanded in custody. A sixth man is reported to have killed himself in a standoff with police in the Chechen capital Grozny.
The suspect threw one grenade at the arresting officers and blew himself up with another, a security source told Interfax news agency.
Mr Nemtsov, a former deputy prime minister and veteran liberal politician, who was 55, was shot in the back four times as he was walking with his girlfriend within sight of the Kremlin. He was buried in Moscow on Tuesday.
Anzor Gubashev and Mr Dadayev, who are both accused of organising and carrying out the murder, were brought into court amid heavy security.
At the scene: Sarah Rainsford, BBC News, Moscow
For a week after Boris Nemtsov's murder there was no word at all on the investigation - no mugshots, no televised appeals, no names. Now five suspects from Russia's volatile North Caucasus have suddenly been presented to a Moscow court, bundled in by heavily armed, masked members of Russian special forces.
Four maintained their innocence and kept their faces covered with paper, under hoods, or with their hands. But investigators say one man, Zaur Dadayev, has admitted involvement. At one point he stopped pacing inside the metal courtroom cage to turn to the TV cameras and declare his love for the Prophet Muhammad.
It could be a red herring, or it could be a clue to the direction this inquiry now takes. Chechnya's leader Ramzan Kadyrov has since claimed that Mr Dadayev was "shocked" by caricatures of the Prophet published by French magazine Charlie Hebdo and by those who supported the cartoonists - including Boris Nemtsov.
But tonight one of the politician's closest allies dismissed Islamic extremism as a motive for his murder. Ilya Yashin told the BBC that Boris Nemtsov had made few comments on the cartoons. He was far better known for his sharp criticism of the Kremlin.
Chechen leader Ramzan Kadyrov said Mr Dedayev was a devout Muslim who was shocked by cartoons of the Prophet Muhammad published by the French satirical magazine Charlie Hebdo.
Russian investigators have previously said they were looking into the possibility that Mr Nemtsov was killed over his defence of the publication.
In a statement on his Instagram account, Mr Kadyrov also confirmed Mr Dadayev had been a member of the Chechen police who was decorated for his bravery.
The other suspects include Mr Gubashev's younger brother Shagid Gubashev and two men named as Ramzan Bakhayev and Tamerlan Eskerkhanov. Reports say all three have denied any involvement in the murder.
Four of the men come from the northern Caucasus region and were detained in the republic of Ingushetia which borders Chechnya, Russian media say.
The Russian Investigations Committee is treating the case as a "contract killing", Interfax news agency reported.
According to the sections of the criminal code cited in court, investigators believe the murder was carried out by a group of people, that it was committed on contract for financial gains, and that it also involved extortion and banditry, Interfax says.
President Vladimir Putin has condemned Mr Nemtsov's murder and called for an end to "shameful" political killings in Russia.
But leading opposition figure Alexei Navalny accused the Kremlin of ordering the assassination to cow the opposition amid Russia's mounting economic problems.
Mr Nemtsov was killed just days before a march against the war in Ukraine that he was organising.
He had also been drafting a report expected to expose covert Russian military involvement in the conflict.