MOSCOW -- The blatant murder of Russian political opposition leader Boris Nemtsov next to Red Square late Friday is rattling President Vladimir Putin's opponents at a time when a once-robust protest movement is on the wane amid a wave of nationalism provoked by Russian involvement in the war in Ukraine.

"The country changed yesterday night," said Dmitry Gudkov, a member of the State Duma, Russia's lower house of parliament, and a main voice of the political opposition. He blamed a culture of "hate" toward opponents of Putin on state-controlled television channels -- the only source of news most Russians have -- for Nemtsov's murder.

"There's your result," Gudkov said in a phone interview Saturday.

But a state representative said the shooting, which eliminated a former political star attempting to stage a comeback with an anti-Putin agenda, "might have been a provocation for destabilizing the country."

Nemtsov was hit by bullets fired from a passing car on a bridge leading to St. Basil's Cathedral and the Kremlin walls, in the very center of the capital. He died on the spot where he was gunned down, according to Russian TV reports. A young Ukrainian woman who was walking with him at the time survived, and she gave statements to police.

"Such an event could be expected," said Lev Ponomaryov, the executive director of the civic group For Human Rights. "Nemtsov's murder didn't happen by chance."

Yet the country woke up Saturday morning to just sporadic coverage of the killing on just a handful of the country's broadcast TV channels, almost all of them government-owned or with ties to Putin's administration. On state-run Channel 1, the 10 a.m. news covered the murder, emphasizing the criminal investigation and highlighting Nemtsov's time as a 30-something political wunderkind, two decades ago.

Then the network switched to a cooking segment with a popular host.

To find serious coverage, Russians had to switch to RBK, a leading business channel sometimes critical of the government. The anchor aired pre-recorded comments from Nemtsov ally and co-organizer in the opposition movement Ilya Yashin, as well as opposition figure Mikhail Kasyanov and Communist Party head Gennady Zyuganov.

A close-up of the flowers piling up at the site of Nemtsov's killing even showed a green and white flyer for Sunday's long-planned opposition rally in Moscow, advertising the demonstration where Nemtsov was expected to speak.

Nemtsov, a one-time political hotshot who became a regional governor and a deputy prime minister under Russia's first elected president, Boris Yeltsin, was kicked out of Yeltsin's administration after the 1998 ruble crisis. He went on to advise Viktor Yushchenko, a Putin adversary who won Ukraine's presidential election and led the Orange Revolution there.

During the past four years, Nemtsov won a job as a regional political official for the western Russian city of Yaroslavl and, more visibly, became a major figure in the nascent protest movement.

That push targeted Putin's grip on power and the country's suffocating political corruption. Nemtsov was a key organizer and speaker at massive rallies that erupted in December 2011 after widespread voting fraud that attracted tens of thousands of Muscovites -- a first for this century in Russia.

But that movement began to lose momentum in May 2012, when police brutally used batons on demonstrators ahead of Putin's inauguration as president for a third term.

After that, authorities filed criminal charges of fomenting civil unrest against a group of ordinary protesters, passed laws enacting enormous fines for unsanctioned rallies and brought various cases against opposition blogger Alexei Navalny and activist Sergei Udaltsov, putting both under house arrest.

The intense upswell of nationalism since last spring, when Russia took over Crimea and pro-Russian rebels formed breakaway republics in eastern Ukraine, crippled the protest movement even further.

The demonstration set for Sunday, nicknamed Springtime, was supposed to publicly denounce the crisis gripping the Russian economy, hurt by falling oil prices and international sanctions imposed for supporting the Ukrainian separatists. Parliament member Gudkov and three other liberal leaders negotiated with Moscow city authorities Saturday to change the official designation of the rally and turn it into a mourning procession, he said.

Without the approval of Moscow's mayor -- who was handpicked by Putin, like all regional governors in Russia -- a rally with an unapproved topic would have been illegal.

In such a climate, many observers said they were appalled, but not surprised, by Nemtsov's killing.

The civic-group leader Ponomaryov, who said he knew Nemtsov for 25 years as a fellow liberal activist, called him "an outstanding politician" and described him as a natural presidential candidate "if we had a democratic [political] system. The typically unsentimental Ponomaryov said in a phone interview that Nemtsov "was brilliant and honest" -- and even called him "a hero ... no question about it."

Putin's statements about Nemtsov's violent death were read out on state media channels and on RBK, where the president said he was taking personal oversight of the criminal case associated with the murder. However, Putin hadn't made any video appeareances as of Saturday night.

As the capital settled into the weekend, two state-owned TV channels presented roundtables Saturday night on the incident, the possible perpetrators and the consequences for the country. The Kremlin-supporting hosts allowed some dissent on the shows. Aleksandr Rutskoi, a former general and a friend of Nemtsov's, called several murder theories "stupid," such as someone targeting the political leader over a personal dispute or radical Islamists attacking him.

The latter theory was one of three offered by Federal Investigative Committee representative Vladimir Markin. Besides the possibility that the killers targeted Nemtsov to cause unrest in Russia, the murder might have been part of an Islamist attack like the one "in Paris" -- meaning the Charlie Hebdo terrorist attack in January -- or might have been committed in connection with the Ukraine conflict, Markin said in a taped comment shown on Channel 1.

By Saturday night, a shoulder-high mound of flowers had been placed at the spot where Nemtsov was shot. The mourning march was scheduled for Sunday afternoon, on a route winding through central Moscow and ending at the bridge where Nemtsov died, organizers said on Facebook and Twitter.

Gudkov indicated the organizers weren't anticipating any provocation by the police, and Ponomaryov suggested participants in the march would be both angry and grieving.

Sunday's rally will be a test of Moscow's feelings toward the killing of a high-level official opposed to the president. If it attracts the cross-section of Muscovites that the 2011 and 2012 demonstrations did -- with liberal intellectuals, working-class people and teenagers side by side -- it would mark a sharp turnaround for the struggling opposition movement, even though one of its main leaders is now dead.