People leave flowers at the site of the killing of Russian opposition leader Boris Nemtsov, in central Moscow, Russia, 28 February 2015.
MOSCOW –Thousands of stunned Russians laid flowers and lit candles on Saturday on the bridge where opposition politician Boris Nemtsov was shot dead near the Kremlin, a murder that showed the risks of speaking out against President Vladimir Putin.
Nemtsov, 55, was shot four times in the back by assailants in a white car as he walked across the bridge over the Moskva River in central Moscow with a Ukrainian woman, who was unhurt, just before midnight on Friday, police said.
Police sealed off the blood-stained bridge close to the red walls of the Kremlin and Red Square for two hours overnight, then hosed it down as people came to pay tribute to one of Putin&39;s biggest opponents over Russia&39;s role in Ukraine.
Flowers were piled at least a metre high, about two metres deep and two metres wide.
A piece of white paper saying "We are all Nemtsov" stood among the flowers.
"People are afraid to support our movement. Opposition activists receive threats every day and Boris was no exception. But they won&39;t stop us," said opposition activist Mark Galperin.
A former deputy prime minister who had feared he would be murdered, Nemtsov was the most prominent opposition figure killed in Putin&39;s 15-year rule.
His gangland-style killing was reminiscent of the chaotic 1990s after the Communist Soviet Union collapsed and raised further questions about the opposition&39;s ability to mount any challenge to Putin in such a dangerous environment.
The Kremlin deflected accusations that it was to blame and Putin called for the killers to be found quickly, taking the investigation under presidential control and denouncing what he said was a "provocation" before an opposition protest on Sunday.
But the killing focused attention on the tough treatment of opponents in Putin&39;s third term, during which several leading critics have been jailed or have fled the country following mass rallies against the president, a former KGB spy, three years ago.
"That a leader of the opposition could be shot beside the walls of the Kremlin is beyond imagination.
There can be only one version: that he was shot for telling the truth," Mikhail Kasyanov, an opposition leader and a former prime minister under Putin, said at the scene.
There was no claim of responsibility, though police were following several lines of inquiry and looking at surveillance camera footage in one of Moscow&39;s busiest and most guarded areas.
Former Soviet President Mikhail Gorbachev cautioned against jumping to conclusions.
"Certain forces will try to use the killing to their own advantage. They are thinking how to get rid of Putin," he said.
US President Barack Obama called for a prompt, impartial and transparent investigation to ensure those responsible were brought to justice for the "vicious killing."