Carrying flowers, portraits and signs that said "I am not afraid," thousands of Russians marched Sunday in Moscow to mourn opposition politician Boris Nemtsov, whose slaying on the streets of the capital has shaken Russia's beleaguered opposition.
Russian President Vladimir Putin has marginalized and intimidated his political opponents, jailing some and driving others into exile, since mass anti-Putin protests swept Moscow in 2011 and 2012. Nemtsov, 55, was among the few prominent opposition figures who had refused to be cowed.
The mourners on Sunday marched to the bridge near the Kremlin where Nemtsov was gunned down shortly before midnight Friday. The mood was somber, with a heavy police presence.
Ilya Yashin, a friend and fellow opposition leader, said he hoped the killing would not frighten people.
"Essentially it is an act of terror. It is a political murder aimed at frightening the population, or the part of the population that supported Nemtsov and did not agree with the government," Yashin told The Associated Press. "I hope we won't get scared, that we will continue what Boris was doing."
The march could energize the opposition, but it could also prove to be a brief expression of emotions that dissipates in a climate of fear.
Russia's federal investigative agency said it was looking into several possible motives for Nemtsov's killing.
The first possibility, the Investigative Committee said, was that the killing was 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."
This suggestion echoed comments by Putin's spokesman and other Russian politicians that the attack was a "provocation" against the state. The consensus of political commentators on state television was that the killing served the interests of Russia's enemies.
Yashin, however, said Russia's leadership and specifically Putin bore full political responsibility for Nemtsov's death.
"It was President Putin who created this atmosphere of hate in our country, the atmosphere of intolerance, which one way or another materialized in the bullet that killed my friend Boris Nemtsov," Yashin said.
As a former deputy prime minister and longtime politician, Nemtsov retained strong ties among Russia's political and business elite, making his killing additionally shocking.
He was killed just hours after a radio interview in which he denounced Putin's "mad, aggressive and deadly policy of war against Ukraine." Nemtsov was working on a report presenting evidence that he believed proved that Russian servicemen were fighting with the separatists in Ukraine, despite official denials.
Yashin said it was unlikely the report would ever be published because investigators who searched Nemtsov's apartment after his death took away his laptop.
Kremlin propaganda had identified Nemtsov as among the leaders of a "fifth column," painting him as a traitor in the service of a hostile West.
TV Center, a station controlled by the Moscow city government, showed a poor-resolution video taken of the bridge from a distance at the time of the killing, which it says shows the suspected killer jumping into a passing car. A snowplow that moved slowly behind Nemtsov and his female companion as they walked on the bridge blocked the view of the shooting.
Another mourning march for Nemtsov was held earlier Sunday in St. Petersburg, drawing what police estimated was 6,000 people.
Nelly Prusskaya, a 66-year-old doctor, said she came to pay her respects to Nemtsov. "I also came to say that I'm against the war in Ukraine," she said. "I'm against political murders."
Most Russians support Putin's policy in Ukraine. Since the annexation of Crimea a year ago, support for Putin has been more than 80 percent.