Five men received long jail terms on Monday for the killing of prominent Kremlin critic Anna Politkovskaya after a trial that did not reveal who had masterminded the Russian journalist's murder.

Politkovskaya, an investigative reporter who uncovered state corruption and rights abuses, especially in Chechnya, was gunned down in the lobby of her Moscow apartment block at the age of 48 on October 7, 2006, President Vladimir Putin's 54th birthday.

The Russian authorities denied any role in the killing, which caused international outrage.

The five men, convicted by a jury last month, exchanged nervous smiles in their glass-fronted courtroom cage before judge Pavel Melyokhin handed down the sentences.

He agreed to the prosecutors' request to order life imprisonment for Rustam Makhmudov, found guilty of pulling the trigger, and his uncle Lom-Ali Gaitukayev, who organised the logistics. The other three received 12, 14 and 20 years.

Mastermind of killing not identified

Politkovskaya was one of nearly two dozen journalists murdered in Russia since 2000, but her case attracted special attention because of the brutality of the contract-style killing and the failure of the authorities - even now, after nearly eight years and several trials — to identify who ordered the assassination.

'They are the lowest level in this criminal chain, which must still be revealed and punished'- Nadezhda Prusenkova, spokeswoman for Novaya Gazeta

Kremlin critics and rights campaigners say the murder symbolizes the weakness of the rule of law in Russia.

"I will be satisfied only when the person or people who ordered this will be sentenced," said Politkovskaya's son Ilya.

Her newspaper, the independent Novaya Gazeta, is still running its own investigation into the killing.

"For as long as the name of the mastermind is not known, there can be no talk of revealing the truth," said its spokeswoman, Nadezhda Prusenkova.

"Today's sentencing is important, but only a step. They are the lowest level in this criminal chain, which must still be revealed and punished."

$145K US in compensation

Makhmudov's two brothers, Ibragim and Dzhabrail, were sentenced to 12 and 14 years in a high-security penal colony for helping to shadow Politkovskaya. The fifth defendant in the year-long trial, former police officer Sergei Khadzhikurbanov, was given 20 years for his part in preparing the slaying.

The court ordered the guilty men to pay 5 million roubles ($145,400 US) in compensation to Ilya and Politkovskaya's other adult child, Vera.

Anna Politkovskaya

Lom-Ali Gaitukayev, left, and Rustam Makhmudov, were both sentenced to life in prison for their parts in the murder of Politkovskaya. Three other men received sentences of between 12 and 20 years. (Pavel Golovkin/Associated Press)

At an earlier trial in 2009, a different jury embarrassed state prosecutors by acquitting three of the five defendants.

Another ex-policeman was separately convicted and sentenced to 11 years in a penal colony, but his trial also failed to reveal the person or people behind the murder.

Putin condemned the murder at the time but infuriated Politkovskaya's supporters by saying her ability to influence Russian politics had been "extremely insignificant" and her killing had caused greater damage to Russia's image than her writing.

The former KGB spy has clamped down on dissent since returning to the Kremlin for his third term in a 2012 election marked by mass protests.

Lev Ponomaryov, a prominent human rights campaigner who worked with Politkovskaya, voiced a widespread belief in Russia that people in the higher echelons of power might have played a role in the killing.

"I am sure the name behind the murder will not be revealed under the current political regime," he said. "If the order came from the ruling elite's senior members, nobody will risk speaking because they know for sure that would cost their life."