The Kremlin has still yet to comment on the murder of acclaimed Russian journalist Anna Politkovskaya.
Ms Politkovskaya, a 48-year-old mother of two, was a vocal critic of Russian President Vladimir Putin.
She earned worldwide fame and numerous awards for her dogged pursuit of rights abuses by Mr Putin's government, particularly in the violent southern province of Chechnya.
She accused him of stifling freedom and failing to shake off his past as a KGB agent.
Russian news agencies quoted mostly unnamed prosecutors and investigators as saying Ms Politkovskaya's political views and her "professional activity" were the main motive behind the murder.
"Such crimes substantially undermine the prestige of any state, and therefore this murder can play right into the hands of the enemies of our state," one police official told Interfax news agency.
In the days before her death, Ms Politkovskaya had been working on a story about torture in Chechnya, which was expected to be published tomorrow, her employer said.
She was shot dead yesterday at her apartment block in central Moscow in a killing prosecutors said was linked to her work.
Former Soviet President Mikhail Gorbachev, a shareholder in Ms Politkovskaya's newspaper Novaya Gazeta, has called the killing a "savage crime and a blow to the entire democratic, independent press".