

Four men accused of helping to organise the murder of the Russian journalist Anna Politkovskaya were today acquitted by a court in Moscow, amid claims by human rights activists that those responsible for her death are still at large.

Two Chechen brothers, Dzhabrail and Ibragim Makhmudov, together with a former Moscow policeman, Sergei Khadzhikurbanov, were cleared of offering her killer operational support. The fourth defendant, Pavel Ryaguzov, a lieutenant colonel in Russia's FSB spy agency, was acquitted in a separate but related case.

Anna Politkovskaya. Photograph: Colin McPherson/Corbis

Politkovskaya, Russia's most famous opposition journalist and a scathing critic of Kremlin power, was shot dead in her Moscow apartment block on October 7 2006. Prosecutors alleged that her assassin was a third Makhmudov brother, Rustam, who they claim has now escaped abroad. The two other Makhmudov brothers staked out her flat before the killing and gave Rustam a lift to the scene, they said.

Friends of the murdered journalist today described the investigation into her murder and the subsequent trial as deeply flawed. Police have apparently been unable to identify the person who ordered Politkovskaya's assassination, while sources at Novaya Gazeta, the paper for which Politkovskaya worked as a special correspondent, have described the case against the accused as "very weak", suggesting the conspiracy was planned at a much higher level.

During the investigation vital pieces of evidence disappeared, including mobile phone SIM cards, computer discs and a photo of Rustam Makhmudov, who apparently fled to western Europe using a false passport. Crucial video footage showing the assassin entering Politkovskaya's apartment block went missing.

The video, shot from behind, shows a narrow-shouldered man wearing a baseball cap. During the three-month trial held at Moscow's district military court the Makhmudovs' lawyer produced mobile phone footage of Rustam swimming in a Chechen river. It revealed he has broad shoulders.

In their final words to the jury on Wednesday, all four defendants insisted they were innocent. During the chaotic and frequently amateurish trial Politkovskaya's son Ilya and daughter Vera sat a few feet from the accused, who were locked inside a yellow metal cage. In a speech to the jury earlier this week, Karina Moskalenko, the lawyer for the Politkovskya family, said the murder had been ordered at a much higher level than the defendants.

"The whole thing has been organised at a high level, not at the level of the accused," she said.

Novaya Gazeta has carried out its own investigation into Politkovskaya's violent death at the age of 48. It has so far refused to reveal its findings. The person most widely suspected of involvement in her death is Ramzan Kadyrov, Chechnya's pro-Moscow president, who is accused of numerous human rights abuses and was a frequent target of Politkovskaya's criticism. He has denied any involvement in her death.

Prosecutors vowed to appeal, claiming the judge had committed numerous procedural violations. The female captain of the 12-member jury read out the unanimous not guilty verdicts after about two hours of deliberations at a military courthouse on Moscow's main souvenir shopping street, the Old Arbat.

When the judge repeated that the defendants were acquitted, relatives of the Makhmudov brothers broke into applause and cries of "bravo". The judge said the defendants were free to go, and they burst out of a courtroom cage and embraced relatives.

"Thank God, thank the jury," said Ibragim Makhmudov, still in the courtroom cage shortly after the verdict. "There was no other possible outcome."

"We're glad," said defence lawyer Murad Musayev. "This is something that happens rarely in Russia. This is what I call justice."

In his final arguments earlier this week, Musayev had accused the prosecution of fabricating evidence and dismissed their case as "dust, fluff and ash".

Relatives and former colleagues of Politkovskaya said justice would not be served until the gunman and the mastermind were prosecuted.

"The investigators now have to start a proper investigation," said Karinna Moskalenko, a prominent lawyer who represented Politkovskaya's family at the trial. "The more time goes by, the harder it gets."