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Alexander Zemlianichenko, Associated Press
A mock street sign carrying Nemtsov's name is placed with flowers at a bridge, where Boris Nemtsov, a charismatic Russian opposition leader and sharp critic of President Vladimir Putin, was gunned down on Feb. 27, 2015 near the Kremlin in Moscow, Russia, Tuesday, April 7, 2015. Supporters of Russian opposition politician Boris Nemtsov gathered at a Moscow bridge where he was gunned down Feb. 27 to commemorate 40 days since his death, a special day in the Orthodox Christian tradition.

MOSCOW — Several hundred people gathered Tuesday just outside the Kremlin walls to commemorate 40 days since the killing of a Russian opposition politician that shook the country.

Boris Nemtsov was shot dead late evening on Feb. 27 as he was walking just outside the Kremlin. It remains unclear who organized the attack.

The bridge where Nemtsov was gunned down was packed Tuesday morning with his supporters, who brought flowers and candles to the spot where he was killed. Passing cars were honking their horns at 11 a.m. local time (0800GMT), a designated moment of commemoration. Some drivers put up pictures of Nemtsov in the windshield as they drove by.

Tuesday marked the 40th day since the politician's killing and is regarded as the final commemorative date in Orthodox Christian tradition.

Nemtsov's killing triggered one of the largest opposition protests in years, with people blaming the Kremlin for fostering a climate of hatred in the country as President Vladimir Putin rallies his support base against what he describes the hostile West.

The politician's close friend and ally, Ilya Yashin, argued Tuesday that Nemtsov's killing was orchestrated in order to "instill fear into that dissenting segment of the society, that segment that does not support the president's policies."

"We want to show that they will not make us scared," Yashin told reporters on the bridge. "We want to show that we will manage to turn Russia into the country that Nemtsov was fighting for, that he died for in the end and that he would not feel ashamed of."

Five suspects, all from the predominantly Muslim republic of Chechnya, have been detained. Supporters of Nemtsov, however, believe that by casting blame on Islamic extremists, investigators are attempting to shift responsibility away from the government and onto a minority with a controversial reputation.

Chechnya suffered two intense wars over the past two decades between Russian forces and separatist rebels increasingly under the sway of fundamentalist Islam. That has reinforced the stereotype among many Russians of Chechens as violent extremists.

The key suspect, Zaur Dadaev, told a court last week that he had been beaten and pressured to confess. Dadaev had been an officer in the Chechen police troops, supervised ultimately by Chechen leader Ramzan Kadyrov.

Yashin told The Associated Press that investigators may have found the man who pulled the trigger but the mastermind is still on the loose.

"Those people directly responsible for organizing the murder are now in Chechnya under protection of Kadyrov and his militia," Yashin said. "If the people who ordered the killing are not sent to prison, they will believe in their own impunity and their right to solve problems in any way they please."