Russian opposition activist Sergei Udaltsov, who was released from prison in August, has been summoned for questioning by federal investigators over the same 2012 protest that landed him in custody.
The Investigative Committee said on September 8 that Udaltsov was questioned as a witness about "individuals who may have been involved in organizing" what the government refers to as "mass disorder" at a May 6, 2012 protest on Moscow's Bolotnaya Square.
Udaltsov said that he had invoked his constitutional right to refuse to answer questions from the investigators.
He told journalists after the questioning that he considered it "unacceptable to testify against anyone, even against those with whom I might have disagreements at this point."
Demonstrators and police blame each other for violence that erupted at the protest against the government and Vladimir Putin, who was sworn in to his current term as president the day after the rally.
Udaltsov was convicted in July 2014 of organizing "mass disorder" at the Bolotnaya Square protest, which led to the prosecution of dozens of protesters in charges rights activists say were trumped up.
The Investigative Committee said it summoned Udaltsov for questioning because of remarks he had made at a press conference following his release from prison on August 8.
At the press conference on August 10, Udaltsov alleged that some opposition leaders might have cooperated with the authorities to incite the violence. He did not name them or give evidence to support the claim.
He said at the press conference that he would not support a presidential bid by opposition politician Aleksei Navalny, who is seeking to run in Russia's March 2018 election.
Election authorities have said that Navalny will be barred from the ballot because of a financial-crimes conviction that he contends was engineered by the Kremlin to punish him for his opposition activity and blunt his challenge to Putin.
Putin has not announced his candidacy but is widely expected to seek and secure a new six-year presidential term in the election.