Russia's NTV channel has broadcast CCTV footage of a suspect

Anna Politkovskaya was found shot dead on Saturday in a lift at her apartment block in the Russian capital, Moscow.

Grainy CCTV footage from the building shows a man in a baseball cap following her inside just before the shooting.

The 48-year-old mother of two was known as a fierce critic of the Kremlin's actions in Chechnya.

Deputy Prosecutor Vyacheslav Rosinsky said that one theory was that the killing had been "linked to the victim's social or professional duties".

Her own newspaper, Novaya Gazeta, suggests on its front page that she was killed for her reporting on Chechnya.

Police sources quoted by Russian media say Ms Politkovskaya was shot three times in the body and once in the head.

A Makarov pistol and four cartridges were reportedly found near her body.

Life of risk

Ms Politkovskaya often wrote about human rights abuses in Chechnya and her last published article in Novaya Gazeta attacked pro-Moscow militia there.

RUSSIA'S CONTRACT KILLINGS Sept 2006 - first deputy chairman of Russia's central bank Andrei Kozlov shot dead in Moscow Oct 2005 - former bank head Alexander Slesarev gunned down near Moscow July 2004 - US editor of Forbes' Russian edition Paul Klebnikov shot dead in Moscow Oct 2002 - Magadan governor Valentin Tsvetkov killed in Moscow Nov 1998 - liberal MP Galina Starovoitova killed in St Petersburg March 1995 - leading journalist Vladislav Listyev shot dead in Moscow

A new article about torture was in the pipeline, according to deputy editor Vitaly Yaroshevsky.

"We were expecting material for Monday's issue," he said on Russian TV.

"She said she would do it and was meant to write this, and perhaps already had. It was about torture in Chechnya."

Ms Politkovskaya had received death threats in the past and suspicions were immediately raised that her death was a contract killing.

Ms Politkovskaya became ill with food-poisoning on her way to report on the Beslan school siege in 2004, which some believed to be an attempt on her life.

In 2001, she fled to Vienna, Austria, after receiving e-mail threats claiming a Russian police officer she had accused of committing atrocities against civilians wanted to take his revenge.

'Brave defender'

Tributes have been pouring in for the campaigning journalist.

Risk is a usual part of my job Anna Politkovskaya Obituary: Anna Politkovskaya Colleagues pay tribute

Former Soviet President Mikhail Gorbachev described her killing as a savage crime, and a blow to the independent democratic press in Russia.

The US state department said America was "shocked and profoundly saddened by the brutal murder of independent Russian journalist Anna Politkovskaya".

The director of the Moscow-based Centre for Journalism in Extreme Situations, Oleg Panfilov, said: "Whenever the question arose whether there is honest journalism in Russia, almost every time the first name that came to mind was Politkovskaya.

"Russia has lost a brave and dedicated human rights defender," said Nicola Duckworth from the rights group Amnesty International which called for a thorough investigation.

Sense of duty

Russian political analyst Anna Zelkina was doubtful there would be results.

Politkovskaya had often received threats

"There is this series of politically motivated murders like hers," she told the BBC.

"I'm afraid that there will be less and less people who would be taking the risk to report... [she's] a very difficult person to replace."

Terry Davis, secretary-general of the human rights watchdog The Council of Europe, suggested she may have fallen victim to "self-appointed executioners... silencing voices of protest".

In an interview two years ago with the BBC, Ms Politkovskaya said she believed it was her duty to continue reporting, despite receiving death threats.