Prosecutor General Yury Chaika's announcement this week that 10 people have been arrested in connection with the murder of Anna Politkovskaya is an encouraging development for those of us who had nearly given up hope that the killers would be brought to justice. But serious doubts remain over whether an objective investigation will be carried out into who hired the gunman to kill her last October.

The investigation into Politkovskaya's murder has led prosecutors to a brutal criminal group that apparently specialized in hired killings. Chaika's description of the group is chilling: a hodgepodge of former and active security officers directed by a Chechen ganglord. Chaika said the group also might have killed U.S. reporter Paul Klebnikov and central banker Andrei Kozlov.

Moscow residents will be able to sleep better knowing that investigators are determined to bust the criminal group. But this would only solve Politkovskaya's murder halfway. The person who hired the killers must also be punished.

Chaika said the mastermind is a Kremlin foe living abroad who wants to discredit Russia, create a crisis here, overthrow the government and bring back "the former system of rule under which money and oligarchs decided everything." He said Politkovskaya had known the mastermind and even met him.

Novaya Gazeta, where Politkovskaya worked, said the findings of its own investigation into her death largely coincided with those of the prosecutors, including the names of the members of the criminal group. But a key difference, it said, is the identity of the suspected mastermind.

While Novaya Gazeta and Chaika refused to name names, there are not many people who fit Chaika's description better than businessman Boris Berezovsky and Chechen rebel envoy Akhmed Zakayev, outspoken Kremlin foes who live abroad and have long been wanted by the Prosecutor General's Office on various charges. Politkovskaya knew both men well, and she met with them in London shortly before her death.

Politkovskaya, however, had many enemies inside Russia -- including some in government circles -- who were interested in silencing her, and investigators should be looking into this as well.

Prosecutors will have to provide proof at some point to substantiate the claim that the murder was ordered from abroad. The Kremlin has long accused foes living abroad of trying to discredit Russia and topple the government. It made such a claim after former FSB officer and Kremlin critic Alexander Litvinenko died of radiation poisoning in London in November.

Prosecutors must thoroughly review the evidence and share it at the appropriate time. Otherwise, questions will linger over whether they carried out an objective investigation or simply built their case around the notion that any action besmirching the Kremlin's reputation must have been ordered by foes-in-exile.