Thousands of Russians marched through Moscow on Sunday shouting slogans such as “Russia will be free!” and “Putin is war!” to mark two years since opposition leader Boris Nemtsov was fatally shot outside the Kremlin.

Nemtsov, a former deputy prime minister, was a fierce critic of President Vladimir Putin. His death on Feb. 27, 2015, in what appeared to be a contract killing, sparked an outpouring of anger and fear in Russia’s beleaguered opposition movement.

The memorial protest was the largest opposition gathering since a similar march for Nemtsov last year. Organizers put the number of participants at just over 15,000.

“It’s very important that after two years people continue to come out and show their solidarity with the ideas for which Boris Nemtsov fought for and gave his life,” opposition activist Ilya Yashin, who was Nemtsov’s friend and colleague, told the Interfax news agency.

Demonstrators carried Russian flags, opposition party banners and placards with quotes from Nemtsov, including “If there’s Putin, there’s no Russia,” and “Our only chance left is the street.” Some carried cardboard Russian flags with bullet holes in them.

“For us, Nemtsov represents freethinking Russia and the democratic values for which we strive: free elections and no corruption,” participant Yekaterina Getgarts said.

Five men went on trial for Nemtsov’s murder in a Moscow military court last year, but no verdicts have been returned in the ongoing case. Investigators allege that the man who shot Nemtsov was Zaur Dadayev, a former officer in an elite Chechen police unit.

But Nemtsov’s family and friends say it was a political hit with a trail that leads to senior officials in the North Caucasus republic of Chechnya, who have not been charged or even questioned.

The Moscow rally largely passed without incident, but an unknown person threw green dye in the face of opposition leader Mikhail Kasyanov. Police made several arrests.

While large crowds are rare at opposition demonstrations in Putin’s Russia, the attendance at Sunday’s rally was significantly lower than a year ago, when organizers estimated that almost 25,000 people took part in the Nemtsov memorial march.

Russia’s opposition has been fragmented in recent years by pressure from the Kremlin, the flight abroad of leading activists and political infighting.

After the march, thousands of people laid flowers on the bridge where Nemtsov was shot in the back several times while walking home with his girlfriend.

Similar demonstrations took place Sunday in other Russian cities, including St. Petersburg and Nemtsov’s home town, Nizhny Novgorod.