Moscow, March 1: About two weeks before he was shot and killed in the highest-profile political assassination in Russia in a decade, Boris Y. Nemtsov met with an old friend to discuss his latest research into what he said was dissembling and misdeeds in the Kremlin.

He was, as always, pugilistic and excited, saying he wanted to publish the research in a pamphlet to be called "Putin and the War," about President Vladimir V. Putin and Russian involvement in the Ukraine conflict, recalled Yevgenia Albats, the editor of New Times magazine. Both knew the stakes.

Nemtsov, a former deputy Prime Minister, knew his work was dangerous but tried to convince her that, as a former high official in the Kremlin, he enjoyed immunity, Albats said.

"He was afraid of being killed," Albats said. "And he was trying to convince himself, and me, they wouldn't touch him because he was a member of the Russian government, a vice premier, and they wouldn't want to create a precedent. Because as he said, one time the power will change hands in Russia again, and those who served Putin wouldn't want to create this precedent."

On Saturday, it was still not clear who was responsible for killing Nemtsov. Some critics of the Kremlin accused the security services of responsibility, while others floated the idea of rogue Russian nationalists on the loose in Moscow.

The authorities said they were investigating several theories about the crime, some immediately scorned as improbable, including the possibility that fellow members of the opposition had killed Nemtsov to create a martyr. Putin, for his part, vowed in a letter to Nemtsov's mother to bring to justice those responsible.

As supporters of Nemtsov laid flowers on the sidewalk where he was shot and killed late Friday, a shiver of fear moved through the political opposition in Moscow.

The worry was that the killing would become a pivot point toward a revival of lethal violence among the leadership elite in Moscow and an intensified climate of fear in Russian domestic politics.

"Another terrible page has been turned in our history," Mikhail B. Khodorkovsky, the exiled former political prisoner, wrote in a statement about the killing.

"For more than a year now, the television screens have been flooded with pure hate for us," he wrote of the opposition to Putin. "And now everyone from the blogger at his apartment desk to President Putin, himself, is searching for enemies, accusing one another of provocation. What is wrong with us?"

Vladimir Milov, a former deputy minister of energy, and co-author with Nemtsov of pamphlets alleging corruption in Putin's government, said he was concerned that the state could now target former officials like Nemtsov - or like him - deemed disloyal.

This comes as analysts of Russian politics say the Kremlin could be worried about, and intent on discouraging, further defections to the opposition, given reported high-level schisms between hard-liners and liberals over military and economic policy. The government is already under strain from Russia's unacknowledged involvement in the war in Ukraine and runaway inflation in an economic crisis.

New york times news service