Moscow police on Thursday released most of the 500-odd people detained during the protest a day earlier demanding action against officials responsible for the arrest of investigative journalist Ivan Golunov, local reports say.
Four of the unnamed protesters are still in police custody.
Several journalists and opposition leader Alexei Navalny were among those freed.
Hundreds of protesters were arrested on Wednesday for taking out the unauthorised march demanding the release of lesser-known reporters languishing in jails for exposing corruption and injustice in society.
Police defended their action saying the protesters rescheduled the June 16 rally without seeking their permission.
The protesters, who were taken by surprise by the sudden release of Golunov on Tuesday (June 12), said they advanced the march to Wednesday to keep up the momentum so that officials responsible for his arrest are punished.
While dropping charges against Golunov and announcing his impending release from house arrest on Tuesday, Interior Minister Vladimir Kolokoltsev said the officers pursuing the case have been suspended and two police generals may be sacked.
The unprecedented mass arrests came on Russia Day (June 12) celebrating the country’s sovereignty after the collapse of the Soviet Union.
For many of the protesters, this special day served as a rallying point for true individual freedom.
Many of them marched wearing T-shirts reading ‘I am/we are Golunov,’ and chanting the repeal of a drug law under which Golunov was arrested on false charges.
They also called for the release of political prisoners.
Opposition politician Alexei Navalny, who had been jailed several times, was among the detained protesters.