Two of five suspects in the killing of Russian opposition leader Boris Nemtsov have been charged with murder and one has confessed, a judge in Moscow said Sunday.

A sixth suspect blew himself up when police tried to detain him in the Chechen capital of Grozny, multiple Russian media outlets reported.

Zaur Dadaev and Anzor Kubashev were formally charged at the hearing Sunday. Judge Nataliya Mushnikova said Dadaev confessed his involvement to the police, the media outlets reported.

Dadaev, speaking from a defendant’s cage in the courtroom, didn’t comment on the confession but asked for a fair trial.

“I am not guilty,” Kubashev told the court, Tass news service reported.

Russian authorities announced Saturday they had detained two suspects from the Muslim-dominated Caucasus region in Nemtsov’s death. Federal Security Service director Alexander Bortnikov said Dadaev served with Interior Ministry troops in volatile Chechnya in the North Caucases while Kubashev worked for a private Moscow security firm.

Ramzan Kadyrov, the Russian-backed leader of the Chechen Republic, is a former separatist who has denounced Russian liberals but denied involvement in the shooting.

The Interfax news agency said investigators believe that Nemtsov was the victim of an extortionist contract killing, but few details on a motive have emerged. Interfax was also among media outlets reporting that a Russian authorities in Grozny on Saturay surrounded a suspect who was killed by a hand grenade that exploded as he tossed it.

Nemtsov, 55, an outspoken critic of Russian President Vladimir Putin, was shot and killed Feb. 27 as he was walking with a female companion near the Kremlin and Red Square.

The other three suspects are Kubashev’s brother Shagit, Ramzat Bakhaev and Tamerlan Eskerkhanov. Eskerkhanov and Bakhaev were ordered held until May 8, Shagit Kubashev until May 7, RT news service reported.

“The suspects denied their ties to the crime, but we have evidence of their guilt,” an investigator told the court, citing forensic evidence and eyewitness accounts. Eskerkhanov claimed to have an alibi, RT reported.

Bakhaev and Eskerkhanov were arrested Sunday outside Moscow, authorities said. The other three were arrested Saturday in the Caucasus region.

Anna Duritskaya, who was with Nemtsov when he was shot, has returned to her native Ukraine but told investigators she would assist the investigation and return to Moscow if necessary, the Russian news agency Tass reported.

Nemtsov rose to prominence in the 1990s as a leader in the drive for capitalism. His fortunes sagged with the emergence of Putin as a political force in the country. His sway had been marginalized — and Putin’s popularity rose — as Russia became more involved in supporting ethnic Russians in Ukraine.

Putin himself has labeled the shooting a “provocation” and suggested Nemtsov was killed by one of Putin’s enemies in an attempt to destabilize the popular government.

Nemtsov was in Moscow to organize a protest against Russia’s involvement in Ukraine and the nation’s current economic crisis. Some of Nemtsov’s supporters and colleagues have pressed for a thorough and transparent investigation of his death.

“For the time being, it’s very skimpy information, which tells us little,” former prime minister Mikhail Kasyanov, who has joined the opposition movement, told Interfax news agency. “But it’s good that the first results of the investigation (have) appeared.”

Contributing: Anna Arutunyan in Moscow