According to police, the Novaya Gazeta journalist, known for her articles criticizing Russian authorities' actions in Chechnya, was murdered Saturday in her apartment building in central Moscow.
Prosecutors earlier said an unknown person clad in black shot Politkovskaya in the chest and head at 17.15 Moscow time (1:15 p.m. GMT), after apparently waiting for the reporter by an elevator in her apartment building on Lesnaya Street.
They also said the killer knew the entry code to her building, and was aware of her movements and her daily time schedule.
"It was a premeditated and well-planned crime," the police source said. "However, it is not clear why the killer did not destroy a surveillance camera and did not attempt to hide his face."
The source said the killer could be simply eliminated by those who ordered the murder.
The investigation considers the journalist's professional activity to be the most probable motive for the crime. However, a police source said a common murder had not been ruled out either.
Investigators continued gathering evidence through the night in Politkovskaya's apartment, and at her office in the Novaya Gazeta premises.
Novaya Gazeta journalists will conduct an independent investigation into the murder of the journalist, who had been providing extensive and independent coverage of the situation in Chechnya since 1999, said Oleg Khlebnikov, the newspaper's deputy editor-in-chief.
The U.S. State Department and a number of international human rights organizations, including Amnesty International and Freedom House, had urged the Russian authorities to conduct a thorough investigation into the murder of the journalist, who was well-known in the West, and bring the perpetrators to justice.
On Sunday, Russia's prosecutor General Yury Chaika took the investigation under his personal control.
The Moscow-based newspaper's shareholders have offered 25 million rubles (about $930,000) for information that could help resolve the murder.
"Shareholders of Novaya Gazeta announced a reward in the amount of 25 mln rubles for any information that could help the investigation," said Vitaly Yaroshevsky, deputy editor-in-chief of the newspaper.