Activist Ivan Skripnichenko died on Thursday of complications resulting from injuries sustained after he was physically assaulted at a makeshift memorial to murdered opposition politician Boris Nemtsov in front of the Kremlin. “Tragedy at the memorial,’’ Andrei Margulyov, another volunteer guard, wrote on Twitter. “Yesterday, Ivan died at Sklife,” he wrote, referring to a Moscow hospital. The exact cause of death is not known.

An unknown assailant punched Skripnichenko and broke his nose late in the evening of Aug. 15. After receiving treatment at Sklifosovsky Moscow City Emergency Care Hospital, he was released and sent home, the Mediazona news outlet reported.

“A few days later, he and I spoke on the phone, and he was going to file a formal complaint with the police,” Mediazona cited Margulyov as saying. “He planned to take a vacation, but instead he checked into the hospital to treat complications from his injury.” Skripnichenko was a regular volunteer guard at the makeshift memorial to Nemtsov, who was shot and killed on the Bolshoi Moskvoretsky Bridge in February 2015 by Zaur Dadayev, a former officer in the Chechen security forces. In July, Dadayev was sentenced to 20 years in prison.

In 2015, following the Moscow government’s refusal to establish a memorial at the site of Nemtsov’s murder, the slain politician’s supporters organized networks to maintain a makeshift shrine, regularly stocked with flowers, pictures, and candles. The city regularly sends police and cleanup crews to remove the memorial and the volunteers who maintain it are regularly harassed by pro-Kremlin activists.

Russian Internet users in February shared footage of one of the sweeps, showing city workers tossing flowers, candles and portraits it into the back of a truck. At the end of the video, a man dressed in civilian clothes then chases down the cameraman, apparently attacking him.