Magnitsky, a tax lawyer for the British investment firm Hermitage Capital Management in Russia, died under questionable circumstances while in custody in 2009 but was prosecuted on tax evasion and embezzlement charges despite what his attorney said was a lack of proof, RIA Novosti reported.
"I never doubted this would be the verdict. I do not believe he was guilty," Dmitry Kharitonov told RAPSI, the Russian legal news agency. "I know he did not commit any crime, and there was no proof to the contrary."
Magnitsky was arrested in 2008 on tax evasion charges after exposing what he said he believed was a $230 million tax fraud perpetrated by Russian officials.
Hermitage Capital head William Browder, a British citizen, was tried in absentia on charges of tax evasion and found guilty. He was sentenced to nine years in prison.
Earlier in July, a Russian prosecutor asked the Moscow court to find Magnitsky guilty but not sentence the dead lawyer. The prosecutor called for a nine-year prison sentence for Browder, who has maintained his innocence.
Hermitage Capital said in a release charges against both men weren't legitimate and it expected guilty verdicts, calling the proceedings a "show trial."
Magnitsky's death and the trial drew sharp criticism from the United States, Europe and Britain.
In December 2012, the United States adopted the Magnitsky Act, which places travel and financial sanctions on Russian officials and others thought to have been involved in Magnitsky's death, the case against him and other human rights abuses.
The European Union reportedly is discussing the introduction of similar measures, RIA Novosti said.
In April, British officials said the trial was contrary to the efforts Russians were making to demonstrate their judiciary's independence and portray the country as attractive for foreign investment.