Thousands of people rallied in Moscow on Sunday to mourn the death of former Russian deputy prime minister and opposition leader Boris Nemtsov, who was gunned down last week.
The rally, which was supposed to be one to protest the Russian policy on Ukraine, and which was to be led by Nemtsov -- one of the staunchest critics of President Vladimir Putin, turned out to be a rally to mourn the slain leader, CNN reported.
Nemtsov, who was the co-chair of the RPR-Parnas party, was shot dead in the intervening night of Friday and Saturday while he was walking near the Kremlin with his 23-year-old Ukrainian model companion Anna Duritskaya.
As mourners gathered near the site of Nemtsov's death, conspiracy theories rented the air.
Ukrainian President Petro Poroshenko had added fuel to the fire by saying on Saturday that Nemtsov was about to reveal information that would have been damaging to Russian interests, CNN reported, citing Ukraine's state-run news agency Ukrinform.
Russian authorities originally declined to issue a permit for the march when it was billed as an opposition rally. However, they agreed to allow the procession honouring Nemtsov, said Mikhail Kasyanov of the People's Freedom Party, of which Nemtsov was a top official.
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The Russian Investigative Committee launched a comprehensive investigation into the incident, and is probing several possible causes behind the assassination, including an attempt to destabilise the political situation in Russia, the conflict in Ukraine and personal animosity.
The committee is also exploring the possibility that the killing is related to the Charlie Hebdo terror attack in Paris or Nemtsov's business activities.
Investigators are tracking leads in the killing and a hunt was on for the killers.
A reward of three million rubles (around $49,000) has been offered for information about the crime, according to media reports.
Putin Saturday pledged to do everything to bring the killers of Nemtsov to justice.
"We will do everything to ensure that the perpetrators of this foul and cynical crime and those who stand behind them are properly punished," Putin said in a condolence message to Nemtsov's mother, according to media reports on Saturday.
However, some of Nemtsov's fellow critics of the Putin government suspected involvement by either Putin's administration or a supporter of the president.
Putin believed that the killing was a contract hit, but one meant to fire up political strife, according to the president's spokesman Dmitry Peskov.
Nemtsov himself had said that he was at a risk of assassination. He had told the Russian newspaper Sobesednik last month that he was "a little bit" afraid his mother's fears that Putin would have him killed would come true.
Critics of Putin are known to have suffered miserable fates in the past.