Magnitsky’s death at the Matrosskaya Tishina jail in November 2009 sparked outrage among international rights groups and drew condemnation from Western governments.

“Deficiencies in the medical care given to Magnitsky have a direct cause-and-effect relationship to his death,” Vladimir Markin, spokesman for Russia’s official investigative authority, was quoted as saying in a statement.

A medical inquiry found that Magnitsky’s death resulted from neglect and investigators planned to soon press criminal charges against prison staff who failed to give him proper care, he added.

The 37-year-old Hermitage Capital investment fund attorney claimed to have unravelled an illegal scheme through which top Russian officials received returns on more than $200 million in taxes paid by the Western firm.

He was arrested shortly after making his claims public and accused of the very crimes he said he had uncovered.

Russian President Dmitry Medvedev earlier this year ordered investigators to probe allegations that Magnitsky was imprisoned on false charges and died of mistreatment in jail.