There were no legal grounds for the arrest of lawyer Sergei Magnitsky, the Presidential Council on Civil Society and Human Rights said in its preliminary conclusion.
Hermitage Capital investment fund lawyer Magnitsky died of heart failure after being denied medical treatment in November 2009. He had been arrested on tax evasion charges just days after claiming to have uncovered massive embezzlement of state funds on the part of law enforcement officials.
The reasons listed by Moscow's Tverskoi District Court can not be considered as grounds for the arrest in line with the Russian Criminal Code.
Russian investigators said on Monday that Magnitsky died because he did not receive medical assistance in a timely fashion.
The council said in a report that Magnitsky could allegedly have died from being beaten.
"Before his death, Magnitsky was deprived of medical care," the report reads. "In addition, there is reasonable suspicion to believe that the death was triggered by beating Magnitsky: subsequently his relatives recorded smashed knuckles and bruises on his body. In addition, there is no medical description of the last hours of his life."
The investigation into Magnitsky's death may be reopened as misinformation in the testimony of Magnitsky's doctor provides grounds to re-investigate this fact, the council said.
Russian President Dmitry Medvedev said on Tuesday that the death Magnitsky in pre-trial custody was caused by criminal actions.
Those responsible for his death will be prosecuted in the near future, Russian Investigative Committee spokesman Vladimir Markin said on Monday.
Magnitsky's death caused public outrage and an international outcry.
The Dutch parliament voted unanimously on Monday for a resolution to impose travel and economic sanctions against Russian officials allegedly involved in Magnitsky's death.