— Hundreds of people gathered in central Moscow Tuesday to remember Russian investigative journalist Anna Politkovskaya on the second anniversary of her killing.

Politkovskaya was shot in her apartment building in an October 2006 killing that investigators have linked to her reporting. She exposed human rights abuses in Chechnya and was critical of the Kremlin.

The killing sparked worldwide outrage and Western governments' demands for an independent and objective investigation.

Four men charged in connection with the killing are to go on trial next week. But the suspect identified by authorities as the triggerman remains at large. Investigators have not said who they believe ordered the killing.

The crowd huddled under umbrellas, encircled by hundreds of police. Former chess champion turned opposition activist Garry Kasparov and opposition politicians Mikhail Kasyanov and Boris Nemtsov also addressed the gathering.

Kasparov called Politkovskaya "honest, courageous and free."

"Such people present the chief threat to Putin's Russia," Kasparov said

Politkovskaya's son Ilya Politkovsky told The Associated Press that holding regular meetings in his mother's honor was crucial.

"These are very important," Politkovsky said. "Then we have the court case coming. We will see what will happen. It is all very important," he said.

The suspects to face trial are Sergei Khadzhikurbanov, a former police officer with Moscow's anti-organized crime unit and brothers Ibragim and Dzhabrail Makhmudov. All deny any guilt.

Because the fourth suspect, Pavel Ryaguzov, is a former Federal Security Service office, the case will be heard at a Moscow military court. Ryaguzov is not accused of direct involvement in the killing but is being tried simultaneously because of his links to Khadzhikurbanov.

Chief investigator Petros Garibyan told Novaya Gazeta in an interview timed to coincide with the anniversary that video surveillance tapes showed the killing had been meticulously planned.

The suspects, he said, were seen entering Politkovskaya's central Moscow apartment building several times before the murder. A third brother, Rustam Makhmudov, who authorities believe pulled the trigger, even held the door open for Politkovskaya when he was leaving the building and she was entering, Garibyan said.