The supposed march rally on Sunday against Moscow's conflict with Ukraine turned into a mourning vigil for one of Russia's greatest opposition leaders, Boris Nemtsov.

Thousands of supporters joined the mourning rally at the vicinity of Kremlin's towers and St. Basil's Cathedral where Nemtsov was shot dead on Friday. People came in droves to lay flowers flowers in the area.

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The 55-year old former deputy prime minister was shot four times by perpetrators who were on board a passing car, a few meters away from a Kremlin tower and in the shadow of St. Basil's Cathedral. The killing occurred a day before a protest rally that was supposed to be headed by Nemtsov.

Moscow Police are still trying to determine the identities and motive of the killers.

Some of Nemtsov's political allies and friends fear injustice over the death of Nemtsov. There are speculations that the the killing is related to his strong opposition against Kremlin and the Ukraine conflict.

As a vocal critic of Russian President Vladimir Putin, others cannot help but speculate if the group of nationalist forces is behind the crime.

During one of his recent interviews, Nemtsov revealed that he feared he would be killed by Putin due to his (Nemtsov) incessant opposition to the Russian Government's stand on war against Ukraine.

"If political views are punished in this way, this country has no future," said Sergie Mitrokhin of the liberal opposition Yabloko Party.

Former liberal politician and now businessman Anatoly Chubais averred that a demand for animosities and aggression came in.

"Several days ago, people were marching with banners saying let's destroy the fifth column. Today, Nemtsov is killed," said Chubais. "Let's stop and think about what might happen tomorrow. Everyone must stop. All of us."

The investigative committee is looking into various angles that led to the death of Nemtsov.

Among the theories are Nemtsov's strong words against the Islamist extremists, the Ukraine conflict, or that he is being utilized as a sacrificial lamb for destabilization plots in Russia. Personal issues are also not being downgraded as possible cause of the killing.

Meanwhile, Putin has called for a thorough investigation on Nemtsov's death and sent a condolence telegram to Nemtsov's mother. In the telegram, the Russian president vowed to do everything to "properly punish" those responsible for the crime.

Nemtsov will be buried on Tuesday in Moscow.

TagsBoris Nemtsov, Russia