At the spot where Nemtsov was killed, a steady stream of mourners came to lay flowers. Sergei Mitrokhin, of the liberal Yabloko Party, said the killing was a blow to all of Russia: "If political views are punished in this way, this country has no future."
Organisers cancelled the protest march and said they would instead meet in central Moscow and march to the spot where Nemtsov was killed.
Putin has taken the investigation into Nemtsov's murder under "personal control" and also sent a telegram of condolences to the slain politician's 87-year-old mother. Putin said of Nemtsov: "He had the task of working in important jobs during the difficult transition period our country was going through. He always stated his positions and argued his points directly and honestly."
There did appear to be an element of genuine shock at the killing among the authorities, with television programmes devoted to the killing featuring some grudging praise for Nemtsov.
Prime Minister Dmitry Medvedev said: "Boris Nemtsov became one of the most talented politicians in the period of democratic transformations in our country. Up to his very last day, he remained a bright personality, a principled man."
But the eulogies from top officials contrasted sharply with previous comments by Putin that the political opposition is a "fifth column" trying to destroy Russia, and repeated television smears calling the opposition traitors.
Anatoly Chubais, a businessman and former liberal politician, said the country was entering a dangerous period. "A demand for hatred and aggression has been created. Several days ago, people were marching with banners saying let's destroy the fifth column. Today, Nemtsov is killed. Let's stop and think about what might happen tomorrow."
4 Lines of inquiry
1.The Russian state body charged with investigating especially serious crimes said it was focusing on several main scenarios, including that the murder was carried out "as a provocation to destabilise the political situation in the country" in which "Nemtsov may have become a kind of sacrificial victim for those who disdain no methods in order to achieve their political aims".
2. The killing was linked to Islamic extremism. This theory was being examined, the committee said, because investigators "had evidence that Nemtsov had received threats in connection with his position on the shooting of journalists from the editorial department of the Charlie Hebdo magazine".
3. "Internal Ukrainian events" led to the assassination. "It is no secret that among both the conflicting sides, there are very radical people, who are not subordinate to any authorities," the committee said.
4. Nemtsov's business activities, a personal vendetta against him or a domestic dispute could also not be ruled out, investigators said. They made no mention of the politician's determined and vocal opposition to President Vladimir Putin's rule, which he frequently characterised as venal, cruel and vengeful.
- Observer, Telegraph Group Ltd