Russia's top investigative agency said Tuesday it is pursuing murder charges against the suspected triggerman and four others in the killing of journalist Anna Politkovskaya, but has failed to determine who ordered the hit.

Politkovskaya, a sharp critic of the Kremlin and its policies in Chechnya, was gunned down in the elevator of her Moscow apartment building on Oct. 7, 2006. The killing drew global outrage and highlighted dangers for journalists in Russia.

Russia's Investigative Committee said it has completed a probe of the suspected triggerman, Rustam Makhmudov, and four others. No date for the trial has been set.

Makhmudov's two brothers and a Moscow police officer have already stood trial, charged with helping stage the killing. But a court acquitted them in 2009. Russia's Supreme Court overruled the acquittal and sent the case back to investigators.

Authorities have since arrested Makmudov and his uncle, Lom-Ali Gaitukayev, who is accused of organizing the killing. The Moscow police officer who faced the initial trial, Sergei Khadzhikurbanov, is still in custody, while the two Makhmudov brothers, Dzhabrail and Ibragim, have been ordered to remain in Moscow pending a new trial.

The committee said it will still try to find out who ordered the murder and look for others who might have been involved.

"It's not the end of it. It's just the case of those five people, and they still don't know the mastermind," Politkovsky's son Ilya said, according to the RIA Novosti news agency.

Politkovskaya was killed on the birthday of Vladimir Putin, who was serving his second presidential term at the time, and that helped fuel speculations about possible involvement of authorities angered by Politkovskaya's exposure of atrocities in Chechnya.