Marchers are gathering in Moscow to remember Russian opposition leader, Boris Nemtsov, who was shot dead on a bridge outside the Kremlin in 2015.
Nemtsov, a reformer, democrat and a deputy prime minister under former President Boris Yeltsin, was a fierce critic of President Vladimir Putin.
Five Chechen men went on trial for the killing in October.
They deny the charges and Nemtsov’s relatives fear whoever ordered the murder will never be found.
Separately on Sunday, anti-Kremlin activist Ildar Dadin, the first person jailed under new laws targeting protests, was released from a Siberian prison. The Supreme Court had overturned his conviction on Wednesday.
He says he was tortured by staff at the prison, an accusation officials deny.
BBC Moscow correspondent Sarah Rainsford reports that crowds are now gathering in the capital for the march in memory of Boris Nemtsov.
Nemtsov was shot in the back as he walked home from a restaurant with his Ukrainian girlfriend late at night near the Kremlin on 27 February 2015.
He had earlier been at the radio station Ekho Moskvy, calling on listeners to join a protest rally that weekend. He had accused Russia’s president of launching an illegal war with Ukraine, prompting Western sanctions and an economic crisis.
He had also been planning to publish a file on Russian involvement in eastern Ukraine.
Tens of thousands marched through Moscow two days after his killing and thousands more attended his funeral.
Nemtsov’s political allies believe the killing was meant to terrify them into silence.
Opposition activist Vladimir Kara-Murza has urged people to join anniversary rallies, which are also expected in St Petersburg and Yekaterinburg.
Mr Kara-Murza is recovering abroad after an illness that left him in a medically induced coma. His symptoms were similar to a near-fatal illness in 2015 that he believed was the result of deliberate poisoning.
The trial of the five Chechens for Nemtsov’s murder began in October.
The suspect who investigators say carried out the killing, Zaur Dadayev, was an officer under the command of pro-Moscow’s Ramzan Kadyrov, the leader of Russia’s Chechen Republic in the volatile North Caucasus.
The Chechen leader has denied any link to the killing.
President Putin called the murder “vile and cynical” and vowed that those responsible would be held to account.
Russia has seen several killings of high-profile politicians and journalists.
But the country has a long history of prosecuting alleged hit-men and then failing to follow the chain of command upwards to discover who ordered the murder or why, our correspondent says.
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