Every weekend Nadezhda Mityushkina comes to the bridge across from the Kremlin and sits down on the low stone parapet at the spot where charismatic opposition leader Boris Nemtsov was gunned down a year ago.

Mityushkina and several dozen other opposition activists and regular Muscovites have been holding vigils at the site for a year now to try to prevent municipal workers or pro-government thugs from destroying the makeshift memorial to Nemtsov, who was shot dead shortly before midnight on Feb. 27, 2015.

The brazen killing sent shivers down the spine of an opposition that had already been marginalized by President Vladimir Putin's systematic crackdown over recent years. While some have been driven into exile or have gone quiet in the year since then, those who stayed have grown increasingly defiant.

"Seven or eight years ago, when people were jailed for 15 days, everyone was terrified, and then people got used to it," said Mityushkina, 53, who works with children with special needs. "Later, people were sentenced to lengthy prison terms, and everyone got used to that, too. Then Boris was killed. If you look at the past years you can see how things got scarier, and for me it was not a turning point but rather a point of no return."

Opposition leaders are increasingly treated like lepers. For example, when Nemtsov's close ally Ilya Yashin was running for a seat in the local legislature in Kostroma outside Moscow last year, local printers refused to produce his leaflets and residents were afraid to canvass for him for fear they would be fired from their jobs.

Anti-Putin protests in the winter of 2011-12 drew 100,000 at their peak, but the numbers then dwindled dramatically as a result of apathy at the lack of progress and fear of arrest. The largest opposition gathering in recent years was a march of mourning held two days after Nemtsov's death.

The Moscow city government has refused to allow the opposition to hold a march past the site of the shooting on Saturday to mark the anniversary, but made a rare concession by allowing the march to take place in another central location. The turnout will serve as a test of the opposition's appeal at a time when Putin's approval ratings are over 80 percent.

Kremlin-controlled media have branded everyone opposing Putin as traitors in the service of a hostile West, and Nemtsov was named one of the leaders of the "fifth column." For the opposition, it is this atmosphere of hatred and intolerance of dissent that made such a killing possible.

Several Chechen men were arrested shortly after Nemtsov's slaying, including five who are due to go on trial this year. The suspected triggerman served as an officer in the security forces of the Moscow-backed Chechen leader, Ramzan Kadyrov.

Nemtsov ally Yashin, who this week released a report on Kadyrov, said he was certain that the killers would not have acted without his approval. Kadyrov has denied any involvement.

Nemtsov's death did not put an end to the incendiary comments about the opposition. Instead, as the one-year anniversary approached, Kadyrov launched a series of stinging attacks on the liberal opposition on his Instagram account, where he has 1.7 million followers.

In language reminiscent of the Stalinist purges, he denounced opposition leaders as "enemies of the people." He posted a video featuring Mikhail Kasyanov, a former prime minister, and fellow opposition activist Vladimir Kara-Murza seemingly in the crosshairs of a rifle. The video appeared particularly ominous as Kara-Murza nearly died last year of what he said was deliberate poisoning.

A week later, Kasyanov had a cake thrown in his face at a Moscow restaurant by a group of men some said were Chechens.

"It always starts with harmless pranks, and when society gets used to the fact that it is OK to behave like that toward opposition leaders ... that means tomorrow you can ratchet up the pressure," said Dmitry Gudkov, the only opposition member in Russia's parliament. "If the government does not crack down on this right now, it will mean that it either has no control of what is going on or that it has a role in it."

Kasyanov said the attacks against the opposition reflect fears by those around Putin that the president's control is slipping. "That's why they are so hysterical about me and my activists," he said.

In spite of the hostility toward them, opposition activists have been fighting to keep Nemtsov's memorial intact. Mourners started bringing flowers, candles and photographs to the Bolshoi Moskvoretsky Bridge on the night he was killed, but municipal workers along with Kremlin supporters have dismantled the memorial repeatedly. Each time, activists have stubbornly brought back new flowers and pictures. One activist set up a website to collect donations and arrange flower deliveries

The government has turned down numerous requests to put up a monument or at least a plaque to commemorate Nemtsov, who in the 1990s served as a regional governor and then a deputy prime minister.

One Moscow official argued that putting up a plaque on the bridge would mean honoring the crime, not the man; another said a monument on the bridge would be a hazard; a third claimed that it would cause controversy since City Hall also is receiving appeals not to put up the plaque.

On Saturday, a week before the anniversary, Mityushkina, 53, and her friends were on the bridge waiting for a flower delivery.

"It's important for us to keep his memory alive," she said. "If you imagine the plaque that should be here, the makeshift memorial is replacing it and we are like nuts and bolts of that plaque to keep it in place."

Before a battered Chevy arrived, packed with tulips and roses, a middle-aged man passed by, laid down a bouquet of white chrysanthemums with a black ribbon on it and quickly walked away toward St. Basil's Cathedral on Red Square.

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Vitnija Saldava, Vladimir Isachenkov and Olga Tregubova contributed to this report.