MOSCOW (AP) -- Leading Russian opposition figure Alexei Navalny was released Friday after spending 15 days in custody and vowed that he and his supporters will not be intimidated by the slaying of a top Kremlin critic.
Navalny, the driving force behind the 2011-2012 mass protests in Moscow, said the killing of opposition leader Boris Nemtsov will not lead him to scale down his campaign against President Vladimir Putin's government.
"This act of terror hasn't achieved its goal, it will not frighten me or my comrades," Navalny said after his release. "We will not reduce our efforts, we will not step back."
Navalny walked free after serving the sentence handed down by a Moscow court, which found him guilty of violating the law when he distributed leaflets in the subway campaigning for an opposition rally. The protest was turned into a mourning march to pay tributes to Nemtsov.
Nemtsov, 55, a former deputy prime minister and one of Putin's most vehement critics, was killed just outside the Kremlin hours after a radio interview in which he denounced the president for his "mad, aggressive" policies in Ukraine. Before his death, Nemtsov was working on a report about Russian involvement in the war in eastern Ukraine.
The West accused Russia of backing the separatist insurgency there with troops and weapons, the accusations the Kremlin denied.
"Our task is to expose those lies and open the Russian society's eyes to Russian soldiers dying on the territory of brotherly Ukraine," Nemtsov's friend, Ilya Yashin, told The Associated Press. Yashin said he and fellow opposition activists had found some of Nemtsov's documents and would try to continue his efforts.
No suspects have been detained in Nemtsov's killing, despite a reward of 3 million rubles (nearly $50,000) offered for information related to the case.
Kremlin critics say the spiteful nationalist propaganda on state television, which cast Nemtsov and other liberals as Western stooges, helped prepare the ground for his killing.
"The atmosphere of mad aggression created by the state television ... has signaled that you could do anything to the people expressing a different view, this will benefit the Motherland," Dmitry Muratov, the editor of the Novaya Gazeta, a newspaper critical of the Kremlin, told the AP.
Yashin also said Putin bears political responsible for Nemtsov's death because he encouraged "hatred, intolerance and aggression toward a part of society that disagrees with the current political course."
Many believe that Nemtsov's death in a tightly secured area near the Kremlin wouldn't have been possible without official involvement, and could be an attempt to scare other government foes.
Putin dubbed Nemtsov's killing a "provocation." The nation's top investigative agency echoed that comment, saying it was looking into whether Nemtsov had been a "sacrificial victim" to destabilize Russia. It added that it was also investigating possible involvement of Islamic extremists because of Nemtsov's support for Paris terror attack victims, a possible Ukrainian link and Nemtsov's personal life.
Nemtsov and other Russians who supported the victims of the Charlie Hebdo shootings had faced threats, Muratov said. "With all possible reservations, I would look in that direction," he added.
He voiced hope for a thorough official probe, adding that the investigator in charge of the case had solved the double murder of a human rights lawyer and a Novaya Gazeta reporter who were killed by extremist nationalists in Moscow in 2009.