Russian investigators on Tuesday dropped their probe into the death in custody of a whistleblowing attorney whose case soured relations between Moscow and Washington.
The investigators said they had no evidence to confirm claims that Sergei Magnitsky had died in 2009 at the age of 37 from beatings by prison officials.
"Based on the preliminary investigation's results, a decision was taken to end the criminal case due to a lack of evidence of a crime," the Investigative Committee said in a statement.
Magnitsky is currently facing a posthumous trial -- Russia's first -- along with his former US-born employer Bill Browder into alleged tax evasion.
The Russian lawyer was jailed shortly after disclosing an alleged $230-million fraud scheme run by senior tax and law enforcement authorities.
An attorney for Magnitsky's mother Natalia said he intended to appeal the decision in court.
"I do not think that you can expect to get justice in today's Russia," Magnitsky's mother said in a statement released by Browder's office.
"It is convenient for someone to hide (the truth)," she added.
Magnitsky's prosecution by the very same officials he had singled out has come to symbolise the Kremlin's failure to crack down on corruption and institute the rule of law as repeatedly promised by President Vladimir Putin.
Browder had hired Magnitsky as an accountant for his Hermitage Capital hedge fund -- the single largest foreign investor in Russia at its height nearly a decade ago.
Magnitsky then discovered an alleged scheme under which officials filed faked documents to receive tax refunds for the funds paid by Hermitage Capital to the state.
Magnitsky died less than a year after being remanded in custody without ever facing trial.
Russian officials attributed his death to chronic ailments that failed to receive proper treatment in detention and opened a probe into medical negligence. No one has been convicted of mistreating the lawyer.
A Hermitage Capital spokesman said the decision "confirms that the Russian state has officially decided to defend those who tortured and killed Sergei Magnitsky."
Russia's human rights community also appeared stunned by the sudden end of a probe that had received international attention and hounded Putin's presidency for years.
"I am amazed by this decision," prominent rights advocate Valery Borshchyov told Moscow Echo Radio.
"It sets a frightening precedent. It makes you think that tomorrow they will be free to brush every death that happens in jail under the carpet."
Browder -- now a British citizen and based in London -- has made it his mission to get Western governments to impose sanctions against Russians implicated in the case.
The United States responded late last year by barring the entry and freezing the bank accounts of dozens of Russians who were believed to have abused Magnitsky's rights.
Russia responded with fury by imposing its own blacklist against US officials and halting adoptions by American families.
The tit-for-tat sanctions saw relations between the two superpowers sink to one of their lowest points during former KGB agent Putin's 13-year rule.
Browder is now lobbying the European Union to adopt similar sanctions against Russia to those imposed by the United States.
The Russians for their part have opened posthumous hearings into the tax fraud allegations against Magnitsky.
His family has boycotted the Moscow trial and refused to send lawyers to hearings that have been repeatedly postponed as a result.
But proceedings were finally launched earlier this month when the state appointed a public defendant to represent Magnitsky and Browder before the judge.
The next hearings have been scheduled for Friday.