But after the Russian opposition figure was gunned down Friday night, Sunday's rally in Moscow took on a different theme. Instead of gathering to criticize Russia's policies on Ukraine, thousands of people came together to mourn the death of the former deputy prime minister.

And as they united near the site of Nemtsov's death, conspiracy theories swirled over who killed the staunch critic of President Vladimir Putin as he walked near the Kremlin with his Ukrainian model companion.

Ukrainian President Petro Poroshenko added fuel to the conspiracists' fire by saying Saturday that Nemtsov was about to reveal information that would be damaging to Russian interests, according to Ukrinform, the state-run news agency.

"A few weeks ago I had a conversation with him on how to build relations between Ukraine and Russia, as we would like them to be. Boris said that he was going to make public the strong evidence for participation of the Russian armed forces in Ukraine. Someone was very afraid of that. Boris was not afraid, the executioners were afraid. They killed him," Ukrinform quoted Poroshenko as saying.

(CNN)