(CNN) -- A whistle-blowing Russian lawyer whose death in custody strained U.S.-Russia relations was posthumously convicted in a tax case in a Moscow district court Thursday, state-run legal news agency RAPSI reported.
Sergei Magnitsky was convicted of tax evasion -- a verdict that comes after he died in 2009 in a Moscow detention center. The United States alleges Magnitsky was beaten to death in detention, a claim that Russian authorities reject.
Magnitsky's 2008 arrest and tax charges came after he uncovered Russia's largest known tax fraud in the form of rebates claimed by government officials who stole money from the state.
The U.S. State Department believes Magnitsky was persecuted because he "was blowing the whistle of confiscation of private assets and misuse of private assets," a State Department official said in a background briefing with reporters earlier this year.
U.S. lawmakers responded to Magnitsky's death by passing the December 2012 Magnitsky Act, a law that imposes visa bans on and freezes the assets of 16 Russian officials that U.S. officials allege were connected to his death, abuse or detention.
Thursday's verdict prompted more criticism from U.S. officials.
"The trial was a discredit to the efforts of those who continue to seek justice in his case," State Department spokeswoman Jen Psaki said. "Despite widely publicized, credible evidence of criminal conduct resulting in Magnitsky's death, authorities have failed to prosecute those responsible.
"We continue to call for full accountability for all those responsible for Magnitsky's wrongful death, and we'll continue to support the efforts of those in Russia who seek to hold those individuals accountable."
Sen. Robert Menendez, the New Jersey Democrat who is chairman of the Senate Foreign Relations Committee, said Thursday that Magnitsky's posthumous conviction "is nothing short of a message to Russia's activist community of the repercussions of opposing the state."
Russia's lawmakers responded to the Magnitsky Act with their own list, slapping similar sanctions on 18 Americans it called rights violators.
Russian President Vladimir Putin last year called the Magnitsky Act "another anti-Russian law" and an "imperialist approach to foreign policy."
In December, Putin signed into law a measure that would ban the adoption of Russian children by U.S. families starting in 2014 -- a move also widely seen as retaliation for the Magnitsky Act.
CNN's Elise Labott, Jason Hanna, Alla Eshchenko, Laura Smith-Spark contributed to this report.