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Ivan Sekretarev, Associated Press
Boris Nemtsov's mother Dina Eidman, center, relatives and friends stand at the coffin during a burial ceremony at Troekurovskoye cemetery in Moscow, Russia, Tuesday, March 3, 2015. One by one, thousands of mourners and dignitaries filed past the white-lined coffin of slain Kremlin critic Boris Nemtsov on Tuesday, many offering flowers as they paid their last respects to one of the most prominent figures of Russia's beleaguered opposition.

MOSCOW — After paying their final tributes Tuesday to slain Kremlin critic Boris Nemtsov, many members of Russia's beleaguered opposition are looking into the future with gloom.

The sadness and loss that drew thousands to Nemtsov's funeral is unlikely to add vigor to the small and marginalized opposition, or dent the broad public support for President Vladimir Putin.

Many believe that his shooting death on a bridge near the Kremlin wouldn't have been possible without official involvement, and that sends a chilling signal to government opponents, who fear it could herald a new, brutal era of reprisals.

Thousands of mourners and dignitaries filed past Nemtsov's white-lined coffin, and many wept as they offered flowers.

"He was our ray of light. With his help, I think Russia would have risen up and become a strong country," said 80-year-old Valentina Gorbatova.

So many came that when the viewing ended after its scheduled four hours, a line still stretched for hundreds of meters (yards) outside the hall named for the Soviet-era dissident and Nobel Peace Prize laureate Andrei Sakharov.

Mourner Marsel Shamsudinov said he had come from Kazan, 700 kilometers (450 miles) east of Moscow, to show that unlike the vast majority of Russians who watch nothing but state-run TV, there are people "who do think and see that the government system is unfair and that we need to change a lot in our country."

But while feelings of anger and grief ran strong at the funeral, few believe that the opposition — fragmented and weakened after years of relentless crackdowns — could pose a serious challenge to Putin, who is supported by 85 percent of Russians, according to recent polls.

Kremlin critics say the virulent nationalist propaganda on state television, which cast the 55-year-old Nemtsov and other liberals as Western stooges, helped prepare the ground for his killing on Friday night.

Nemtsov had been a deputy prime minister under Russia's first elected president, Boris Yeltsin, who touted him as his likely successor before opting instead for Putin. Although his influence in mainstream politics vanished, Nemtsov had remained one of Putin's most vehement critics. In a radio interview a few hours before his death, he denounced the president for his "mad, aggressive" policies in Ukraine.

Putin dubbed Nemtsov's killing a "provocation," and nationwide TV networks quickly picked up the theme, blaming Western intelligence agencies, Ukrainian agents or even the opposition. They focused heavily on a 23-year-old Ukrainian model who was with Nemtsov when he was slain, with some suggesting their relationship could be a motive.

The nation's top investigative agency echoed Putin's comments, saying it was looking into whether Nemtsov had been a "sacrificial victim" to destabilize Russia. It said it was also investigating whether Islamic extremism, the Ukraine conflict and Nemtsov's personal life were possible motives.

No suspects have been arrested. Divers searched for the gun in the Moscow River under the bridge where Nemtsov was killed by four shots in the back.

The area is always packed with uniformed and plainclothes agents and security cameras, making it hard for any attacker to go unnoticed. Kremlin critics say Nemtsov, like other prominent opposition figures, was under close surveillance, implying possible official involvement in the assassination.

Among those mourning Nemtsov were U.S. Ambassador John Tefft; Russian Deputy Prime Ministers Sergei Prikhodko and Arkady Dvorkovich; tycoon Mikhail Prokhorov, the owner of the Brooklyn Nets who ran against Putin in 2012; and Yeltsin's widow, Naina.

Former Prime Minister Mikhail Kasyanov, who has joined the opposition, also was there, as was Nadezhda Tolokonnikova of the dissident punk group Pussy Riot.

But Polish and Latvian lawmakers were prevented from entering Russia for the funeral. They were on a list of officials barred from the country in retaliation for European Union sanctions against Moscow in the Ukraine crisis.

Russia's leading opposition figure, Alexei Navalny, also was not allowed to attend because he is serving a 15-day jail term for unauthorized leaflet distribution.

Navalny has bluntly accused Putin of ordering the killing to scare the opposition. "Fear must grow and economic problems should be compensated by police controls," he wrote on his blog.

Navalny was a driving force behind anti-Putin protests in 2011 and 2012 that drew more than 100,000 into Moscow's streets. The wave of demonstrations abated after Putin began a crackdown on dissent following his re-election to a third term in March 2012, with repressive new laws and arrests of activists.

Navalny has a following in the capital, as does Mikhail Khodorkovsky, an oil tycoon who spent 10 years in prison for challenging Putin's rule and left Russia after his release in December 2013. Navalny's energy and charisma, and Khodorkovsky's wealth and entrepreneurial talents make them the two most prominent opposition leaders, but neither has a chance to expand their support base quickly beyond the urban middle class in Moscow and a few other big cities.

Alexei Malashenko, a researcher with the Carnegie Endowment's Moscow office, wrote that Nemtsov's slaying would be unlikely to re-energize the opposition, which "will remain as incoherent as before and will pose no threat to the regime."

Russia's annexation of Ukraine's Crimean Peninsula a year ago helped further swell Putin's popularity amid a wave of increasingly spiteful nationalist and anti-Western propaganda on state television. With Russia's economy plunging into recession under slumping oil prices and Western sanctions, Putin has sought to shift the blame and portray critics of his Ukrainian policy as "national traitors."

The government also has backed nationalist groups, which have threatened reprisals against liberal foes of the Kremlin.

Veteran human rights activist Lev Ponomarev, echoing many opposition figures, said the strong nationalism and intolerance of dissent under Putin has coarsened society and encouraged violence.

"In this atmosphere of violence and hate, these killings will only continue," he said.

Some say Putin may have lost control of the situation after giving his blessing to the rise of violent nationalism.

Respected political scholar Georgy Mirsky said some members of extremist nationalist groups could have reckoned that killing Nemtsov might force Putin to abandon any compromise with the West over Ukraine and take a harsher path.

"They want the government to conduct a tougher and more consistent course, stop fearing to openly send troops into Ukraine, and provoke the West," he wrote in a blog.

Mirsky added that extreme nationalists may have the support of some law enforcement officials.

Alexander Baunov, a Carnegie researcher, said the killing could reflect a high-level battle over the direction the country should take.

"It's clear that in the Russian elite there are supporters of the soft approach and supporters of the tougher approach," he told The Associated Press. "There are forces that want to force Russia into greater isolation and take a tougher approach against the opposition at home."

Putin has ordered heads of law enforcement agencies to personally oversee the Nemtsov investigation. He has promised the opposition leader's 86-year-old mother Dina Eidman — who stood mournfully before his coffin at Troekurovskoye cemetery — that the killers would be tracked down.

Few expect the probe to point at the real culprits, however, especially if the links go to high echelons of the government.

"Even if you think about the government as a kind of leviathan, there are still different parts of the leviathan," Baunov said. "It's very difficult, very painful, for the leviathan to cut off its own tail."