March planned to honor Nemtsov

Thousands of people laid candles at a bridge near the Kremlin in central Moscow, where an unidentified assailant shot multiple times at Nemtsov on Friday night.

"The march in the Marino district which we had planned - a positive march with flags and balloons - does not fit this tragic moment and the magnitude of Nemtsov's persona, as well as the magnitude of the red line we have now crossed and which we have not recognized," Leonid Volkov, one of the organizers of Sunday's rally told Reuters news agency.

Moscow city authorities approved the march, scheduled to begin at 3 p.m. local time (1200 UTC), allowing a maximum of 50,000 people.

Motives for Nemtsov's murder

United Nations Secretary General Ban Ki-moon condemned the murder. "The Secretary General was shocked by and condemns the brutal killing of Boris Nemtsov in Moscow on February 27," a statement said, adding that Ban "notes that an investigation into this murder has been announced and he expects the perpetrators to be brought to justice."

Investigators said they were looking into several motives leading to the 55-year-old's murder. A committee told journalists that the murder could have been aimed at destabilizing the political situation in Russia and Nemtsov was a "sacrificial victim for those who do not shun any method for achieving their political goals." Earlier, President Vladimir Putin had described the murder as a "provocation" for the Russian state.

Officials were also looking into the possibility of a personal motive to kill Nemtsov, who was reported to have been dating a Ukrainian model 30 years younger. The agency also speculated on Nemtsov, a Jew, being a target of Islamists, who had been offended by the leader's repeated criticisms of the Charlie Hebdo attack in Paris.

A critic of Putin

Nemtsov served as a regional governor and deputy prime minister in the 1990s under former President Boris Yeltsin's government. He was once seen as a possible successor to Yeltsin before Putin took over the country's reins.

The leader was believed to have been working on a report which presented evidence of Russia's direct involvement in the Ukraine crisis. In a previous report, Nemtsov had also alleged that Russian officials had stolen $30 billion (27 billion euros) during the Winter Olympics in Sochi last year.

His killing came a few hours after a radio interview in which he called upon Moscow residents to join the opposition's protest rally on Sunday and criticized Putin's "aggressive and deadly policy of war against Ukraine."

mg/bk (Reuters, AP)