Another arrest – but will we ever know who wanted Anna Politkovskaya dead?

Russia announced yesterday that a former police officer had been charged with organising the murder of Anna Politkovskaya, the crusading journalist who was shot dead outside her Moscow flat in 2006.

The Investigative Committee said Dmitry Pavlyuchenkov, a lieutenant colonel in the police at the time of the murder, has been charged with planning the killing. He is alleged to have tracked the journalist's movements using the cover of police work, in order to help the killers.

There has already been one trial over the murder, with the suspects acquitted of helping to organise the hit, and friends and colleagues of Ms Politkovskaya expressed scepticism that the latest charges were a real breakthrough. "Even if Mr Pavlyuchenkov did organise the killing, it's very unlikely he was the one who ordered it," said Tanya Lokshina of Human Rights Watch in Moscow. "We need to see not only the killers, or the technical organisers, but also the mastermind brought to justice."

The killing of Ms Politkovskaya, who was well known for her searing reports from Chechnya, drew a wave of condemnation from across the globe, but nearly six years later nobody has been brought to justice for her murder. She worked for Novaya Gazeta, part-owned by The Independent's financial backer, Alexander Lebedev, and the last leader of the Soviet Union, Mikhail Gorbachev. The paper specialises in investigative reporting, and several of its journalists have been assassinated.

According to the Investigative Committee, Pavlyuchenkov was engaged by a Chechen criminal authority, who in turn had been hired by someone who was angry about the nature of Ms Politkovskaya's reporting from Chechnya. The report does not name this person.

Many observers have pointed the finger of suspicion at Ramzan Kadyrov, the Kremlin-backed ruler of Chechnya. Many of Ms Politkovskaya's investigations uncovered allegations of torture and abuse at the hands of militias loyal to Mr Kadyrov. The Chechen leader, however, has always vehemently denied any suggestion of involvement in the crime.

Shortly after Ms Politkovskaya's death, President Vladimir Putin, in an attempt to show that the state had no motive to carry out the murder, dismissed her work as "extremely insignificant" and said Russia's image was harmed more by her murder than by her work. As such, Russian officials have hinted that Boris Berezovsky, a London-based exile and a critic of Mr Putin, might have ordered the murder in an elaborate plot aimed at making the Kremlin look bad. Mr Berezovsky denies any links to the case.

Ms Politkovskaya's murder is the highest profile of a number of assassinations of journalists and activists in recent years, almost all of which have gone unsolved. Particularly vulnerable are investigative journalists working in Russia's volatile North Caucasus region, as Ms Politkovskaya was.

Sunday marked the three-year anniversary of another high-profile murder, that of the human rights activist Natalia Estemirova, who lived in Grozny and often worked on stories with Ms Politkovskaya. Ms Estemirova was kidnapped as she left her house for work, and was found dead a few hours later in neighbouring Ingushetia.

Ms Lokshina of Human Rights Watch said: "It has been nearly six years since the murder of Politkovskaya, and in all that time our question has remained the same: who ordered it? Since then there have been other killings too. The work these people were doing and the failure to catch the perpetrators points to the involvement or at least the acquiescence of state officials."