Her newspaper, the bi-weekly Novaya Gazeta, revealed on Sunday that she had been preparing an article on torture in Chechnya for Monday's edition.
"She had several important photographs which showed all of this. This was her material. It was going to be published in Monday's issue. We have some of her notes and, of course, we will partly publish this material," Dmitry Muratov, editor-in-chief said.
Mikhail Gorbachev, the former Soviet president, and part owner of the newspaper where Politkovskaya worked, described her killing as "savage" and "a blow to the entire democratic, independent press", Russian news agency reported on Sunday.
The US and the Council of Europe joined Russian politicians, journalists and human rights activists in condemning her murder at her home in central Moscow on Sunday.
Police said that her execution-style murder could have been in connection with the victim's social or professional duties.
Politkovskaya, 48, was shot in her apartment building. The killer first fired at her chest, then her head, police said.
Police released security camera footage showing the main suspect, a man wearing dark clothing and a dark baseball cap.
Investigators were examining Politkovskaya's body and a 9mm Makarov pistol found at the scene, the Moscow prosecutor's office said.
"Politkovskaya, was the 42nd journalist killed in Russia since since Vladimir Putin, the current Russian president came to power in 2000"
Committee to Protect Journalists
Prosecutors also removed for examination two box loads of documents from her office at the bi-weekly Novaya Gazeta, as well as her computer hard-drive and diary.
She had received several prizes for her daring investigations, including the Russian Union of Journalists' Golden Pen award and the Journalism and Democracy award from the Organisation for Security and Cooperation in Europe.
She was also the author of several books critical of the Russian authorities including Dirty War: A Russian Reporter in Chechnya, and Putin's Russia.
Her reportage stood out increasingly in a country where, after Putin's rise to power, journalists have all but abandoned criticism of the Kremlin or the conflict in Chechnya.
Oleg Panfilov, at the centre for Journalism in Extreme Situations, said: "There was always a constant feeling something would happen to her."
Russia's public chamber, an officially backed civil society body, described her murder as "a blow at the most important institution of democracy - free speech".
Sean McCormack, the US state department spokesperson, said that the US was "shocked and profoundly saddened by the brutal murder".
"The United States urges the Russian government to conduct an immediate and thorough investigation in order to find, prosecute, and bring to justice all those responsible for this heinous murder," he said.
Alu Alkhanov, Chechnya's Russian-backed president, also voiced outrage and regret at Politkovskaya's murder, urging investigation and punishment of "all who stood behind this".
"Though our views on what is happening in Chechnya were completely different, Politkovskaya was not indifferent to the Chechen people's fate," Alkhanov said.
Calls for transparencey
The Organisation for Security and Cooperation in Europe (OSCE) stressed the need for a thorough and transparent investigation, given Russia's poor record in resolving crimes against reporters.
"It is extremely important to break the circle of inconclusive investigations in regard of the recent murders of journalists in Russia," Miklos Haraszti, the OSCE's media freedom representative said.
A man holds a picture of
Politkovskaya during a rally
Joel Simon, director of the Committee to Protect Journalists, described Russia as "one of the most murderous places in the world for journalists and it has a long history of impunity in these killings".
"This is the time for Russian authorities to reverse this years-long assault on independent journalism by bringing Anna Politkovskaya's killers to justice."
According to the New York-based Committee to Protect Journalists, Politkovskaya was the 42nd journalist killed in Russia and the 12th reporter to die in a contract-style murder since Vladimir Putin, the current Russian president, came to power in 2000.