Two Russian policemen who were among 10 people arrested over the murder of journalist Anna Politkovskaya have been released, Russian media report.
Politkovskaya's hard-hitting reports exposed official abuses
Another suspect in the group, a Federal Security Service (FSB) officer, was arrested on an unrelated charge.
Campaigners for press freedom and former associates of Politkovskaya are sceptical about Prosecutor General Yuri Chaika's murder plot theory.
He spoke of 10 arrests in Russia, but said the plot had been hatched abroad.
Politkovskaya was a vehement critic of President Vladimir Putin - especially his military campaign in Chechnya. She was shot dead near her Moscow apartment last October.
"The individuals interested in eliminating Politkovskaya can only be ones living beyond Russia's borders," Mr Chaika told reporters on Monday.
He said plotters abroad had controlled a Chechen gang boss and several serving or former security officers in Moscow suspected of murdering Politkovskaya.
The chief prosecutor was shown briefing President Putin on the case
He blamed conspirators interested in undermining President Vladimir Putin's authority and destabilising Russia.
The BBC's Russian affairs analyst Steven Eke says officials have strongly implied that Boris Berezovsky, the fugitive billionaire businessman living in London, was behind the plot.
Mr Berezovsky described the implication as "absolutely mad".
The official version now appears to be unravelling, our analyst says.
One suspect was already in prison at the time of the killing.
It has also emerged that one of those held had previously testified against police in a separate case involving torture and murder.
Her son, Ilya Politkovsky, told Reuters news agency that Mr Chaika's announcement was politically motivated.
A prominent journalists' organisation in Moscow - the Centre for Journalism in Extreme Situations - has called the official version a fabrication.
The murder of Politkovskaya drew international condemnation, including allegations that President Putin was failing to safeguard freedom of speech.
Politkovskaya made her name reporting from Chechnya for Russian daily, Novaya Gazeta.
She was also the author of two books translated into English, A Dirty War: A Russian Reporter in Chechnya (2001), and Putin's Russia (2004).
Her writing was often polemical, as bitter in its condemnation of the Russian army and the Russian government as it was fervent in support of human rights and the rule of law.