Formal charges were filed Wednesday against four men accused in connection with the 2006 killing of journalist Anna Politkovskaya, Russian investigators said. Three men were charged with involvement in Polikovskaya's murder while an officer from the Federal Security Service, the FSB, faces charges of extortion and abuse of office, the Investigative Committee said in a statement. The four have been held since their arrests last August. Politkovskaya, 48, was shot to death in her central Moscow apartment building in October 2006. Colleagues believe her murder was linked to her work reporting on abuses by Russian troops in Chechnya. One suspect, Sergei Khadzhikurbanov, is a former police officer. Two others, brothers Dzhabrail and Ibragim Makhmudov, are from Chechnya. The committee said the charges against the FSB officer, Lt. Col. Pavel Ryaguzov, relate to other crimes. It wasn't immediately clear whether Wednesday's charges were somehow connected to Politkovskya's murder. Authorities previously have accused Ryaguzov of giving Politkovskaya's killers her address. The committee did not cite an alleged motive for Politkovskaya's killing or specify the suspects' roles in her murder. A separate probe into the suspected shooter Rustam Makhmudov, who remains at large, will continue, the Investigative Committee said Wednesday. He is the oldest of the Makhmudov brothers. Charges against several others, including former Chechnya district administrator Shamil Burayev, were dropped, the committee said. Politkovskaya's colleagues at the Novaya Gazeta newspapers accused authorities of deliberately undermining the investigation by releasing details about the case before it reaches trial. Novaya Gazeta editor Dmitry Muratov said Wednesday that leaks from investigation allowed the accused shooter to escape arrest, the Interfax news agency reported. Muratov called it too early to consider the murder solved. Russian officials have alleged that Politkovskaya's killing was ordered by someone living outside Russia with the aim of discrediting the Kremlin - statements that have been interpreted as alluding to Boris Berezovsky, a former Kremlin insider who lives in London and is now a fierce Kremlin critic. Berezovsky, wanted in Russia on embezzlement and other charges - all of which he denies as politically driven - has said he had nothing to do with Politkovskaya's death. Novaya Gazeta has said the mastermind is likely in Russia.