The Investigative Committee also cautioned however that it still had no clear picture about who ordered the killing: an admission that rights groups say hides the state's refusal to prosecute the high-ranking officials involved.
Politkovskaya was gunned down in the elevator of her Moscow apartment building by a waiting assailant who fled the scene and was only partially filmed by a closed circuit camera.
The Novaya Gazeta paper for which she worked said it believed her murder was ordered by people close to Ramzan Kadyrov -- the strongman leader of Chechnya whom she was investigating for allegedly torturing his foes.
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The Investigative Committee said it now believed that top former Moscow policeman Dmitry Pavlyuchenkov helped organise Politkovskaya's murder and helped track her movements for months.
The former head of the Moscow police surveillance department was arrested on August 23 and has since faced a series of different charges while continuing to deny all responsibility.
"Between July and September 2000, Pavlyuchenkov established the victim's place of residence, the route she takes (home), and reported this information to other members of the organised crime group," the committee said in a statement.
"Moreover, he obtained the weapon and ammunition that were later used in the killing," the statement added.
The account is one of the most detailed to date of what officials believe happened in a case that drew strong Western pressure on President Vladimir Putin to lift restriction on media and human rights.
The Investigative Committee said Pavlyuchenkov was working for a man it identified as Lom-Ali Gaitukayev who is now serving 12 years in prison for the attempted murder of a businessman.
A senior editor at Novaya Gazeta had earlier said he believed Gaitukayev had once either worked for Russia's Federal Security Service that Putin ran before becoming prime minister for the first time in 1999.
The Investigative Committee stressed that it had no idea at this stage who asked Gaitukayev to hire the Moscow policeman to organise the attack.
