Stanislav Markelov, a human rights lawyer gunned down in central Moscow after frequently challenging the actions of Russian authorities, was buried Friday.

Rights activists and former intelligence officials compared last Monday's murder of Stanislav Markelov by a masked gunman to the 2006 slayings of journalist Anna Politkovskaya and former security officer Alexander Litvinenko, who also fell afoul of the authorities. Some accused Russian security agencies of involvement with Markelov's killing.

Anastasia Baburova, who like Politkovskaya reported for Novaya Gazeta, also was fatally shot in the attack, which occurred shortly after Markelov left a news conference. Her funeral was also held Friday in Moscow.

With a strong police presence outside the gates of the Ostankino Cemetery in northern Moscow, dozens of mourners lined up under an icy rain to throw earth on Markelov's coffin and lay flowers at his freshly dug grave.

As the coffin lay open to let relatives bid a final farewell, Markelov's brother Mikhail, a former State Duma deputy with the Rodina party, leaned down to kiss his brother's brow then straightened up slowly and wept silently.

Rights activist Lev Ponomaryov, who once leased office space to Markelov, said his killing was the latest signal that Russia is sliding back toward Soviet-era repression. "The murder shows we are in a post-totalitarian state that is returning to its old ways," Ponomaryov said. "There have been political murders, and they will continue."

Mikhail Metzel / AP People paying their last respects to murdered human rights lawyer Stanislav Markelov during a funeral on Friday.

Genri Reznik, one of Russia's most respected lawyers, said Markelov "understood the threats he faced, but he banished fear from his soul."

The case has been brought under the control of federal investigators, and their chief, Alexander Bastrykin, vowed Thursday to punish those accountable.

But others expressed concern that it will go unpunished, like the killings of several Kremlin critics who sought to expose rights abuses and wrongdoing by the Russian state -- and whose slayings prompted allegations of official involvement. "Those who ordered [the murder] are the same as those responsible for murdering Litvinenko, Politkovskaya, Shchekochikhin and others," former Russian security agent Yevgeny Limarev, a witness in the Litvinenko case who fled to Europe in 1995, said in e-mailed comments. "The list is very long."

Yury Shchekochikhin, who investigated alleged high-level corruption for Novaya Gazeta, died in 2003 after a brief, mysterious ailment.