Moscow, Russia - On a cold, rainy October morning, Moscow's Red Square was almost deserted. As I was making my way towards the Moscow River along the Kremlin's eastern wall, the light rain turned into a steady downpour.

By the time I stepped onto the Bolshoy Moskvoretsky Bridge, gusts of strong northerly wind were making it difficult even to hold on to my umbrella.

I was looking for something I wasn't sure I would find: a sign marking the place where Russian opposition leader Boris Nemtsov was fatally shot on February 27, 2015.

What I found was more than a sign: a dozen neatly arranged flowerpots lined the pavement of the bridge. In between the pots were black-and-white portraits of Nemtsov.

I looked around: there was no one on the pavement, except me and an elderly man with a bushy white beard and a long khaki raincoat sitting on a small stool.

I found it odd that he was just sitting there in the pouring rain. I thought perhaps he was selling something, so I approached him.

"No, I'm on shift," he said. "They destroy the memorial, so we keep watch here to make sure it doesn't disappear."

His hands emerged from under his raincoat. He took off his black mittens and introduced himself: Grigory Saksonov, a human rights defender.

He is part of a small group of concerned citizens who call themselves the Nemtsov Bridge and who have established a 24-hour watch over the makeshift memorial.

They decided to do so after there were attempts shortly after Nemtsov's death to remove the memorial.

Since then it has been attacked a number of times by right-wing activists and also regularly removed by the municipal cleaning service.

Moscow's local authorities have refused to allow the installation of a plaque in the memory of Nemtsov and have rejected suggestions to rename the bridge to bear his name.

I asked Saksonov if he was a friend of Nemtsov. No, he wasn't, and he didn't even know him personally, Saksonov replied. Then why sit here in the cold rain?

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"We are here because our hope is that people will wake up," he said. "They are killing all our democrats. And they are calling us the fifth column, calling us traitors."

Nemtsov's murder has been the latest in a string of political assassinations in Russia since the early 2000s.

He, like other opposition figures with liberal and democratic views who opposed the war in Ukraine, had been called "the fifth column" by conservative commentators and Kremlin loyalists.

Just before his death, Nemtsov was working on a report detailing Russia's military involvement in the Ukrainian war, which the Kremlin refuses to admit to this day.

In June this year, a Moscow court sentenced five Chechens for Nemtsov's murder. Zaur Dadaev, who shot him, received 20 years in prison and his four accomplices were handed jail sentences between 11 and 19 years.

Dadaev is a former military officer in the Chechnya-based Sever battalion, which Nemtsov had mentioned in his report as being deployed to the Donbas region of Ukraine in 2014.

Shortly after Dadaev's arrest, Chechen leader Ramazan Kadyrov wrote on Instagram that he knew him as a "genuine Russian patriot […] who couldn't have made a step against Russia", suggesting that he, as a religious man, must have been upset over Charlie Hebdo's anti-Muslim cartoons and Nemtsov's support for the French magazine [Nemtsov had written a very short blog post on the topic that had not really attracted much public attention].

After initially admitting to the murder, Dadaev later claimed he was tortured into confessing.

Criminal conviction

In June this year, Nemtsov's daughter Zhanna, said in an interview that he had a plan to run in the 2018 presidential elections.

Unlike opposition leader Alexei Navalny, who is likely to be disqualified because of a past criminal conviction, Nemtsov wouldn't have had legal problems to stop him running and challenging Vladimir Putin's presidency.

After his death, he became even more of a political symbol for Russians opposing the current government.

"His ideas are close to us: democracy, [democratic] transfer of power," said Tatyana Kozlova, who, along with another volunteer, Evgeny Mishchenko, had taken over the watch from Saksonov.

It was 8:30pm, and the rain had now become a light drizzle.

Kozlova, who works as a courier, said she did not support any particular party and also did not know Nemtsov personally.

"They don't like this [memorial] under the walls of the Kremlin. It is reminding them, it is like a needle in the eye for them," she said.

As I waved goodbye to Kozlova and Mishchenko, they told me to come back for the overnight shift. There would be two poets guarding the memorial.

At midnight I was back, and there were indeed two poets standing guard: Alexei Mikheev and Andrei Margulev.

"The night, like a ship worker, pulls the ropes of the dawn, the pillow had turned into a stone from sleeplessness, the summer threatened a terrible death, these children have played a game of war," Mikheev said, reciting one of his poems dedicated to the 2012 anti-government protests that he attended in Moscow.

He said he came every week from the city of Perm (about 1,400km from Moscow) just to do the overnight shift at the memorial. For him, it's an opportunity to hang out with like-minded people who oppose the current government.

Margulev explained that the vigil at the memorial, which began shortly after Nemtsov's death, has persisted despite regular harassment.

The group has lost one member, Ivan Skripnichenko, who was struck in the face by an unidentified man at the memorial.

Fatal assault

Skripnichenko died a week later in a hospital where he was supposed to have surgery on his broken nose.

He was one of a number of Kremlin critics who have been physically assaulted in the past few years by ultra-nationalist activists.

The authorities did not open a formal investigation into Skripnichenko's case. His photo now can be seen at the memorial.

His death, however, has not weakened the determination of the group.

"In the winter, in - 25C, strong northern wind and 90 percent humidity, there will be a person here on shift. Perhaps it is difficult for you to imagine?" Margulev told me.

It is indeed, I replied.

He said the vigil is not just about Nemtsov and his murder.

"We do this so we can clear our conscience. This is our fight. This is all we can do so we don't become like those who are ruling us right now," Margulev said.

He said the group would continue the vigil at Nemtsov's memorial until the authorities allow a plaque to be installed on the bridge.

Follow Mariya Petkova on Twitter: @mkpetkova