Relatives and friends on Friday buried Sergei Magnitsky, the key witness in a tax fraud battle whose sudden death in prison prompted an outcry from rights activists.

Prosecutors said Magnitsky, 37, died Monday of heart failure. Mourners blamed the country’s notorious prison system for not properly attending to the medical needs of the lawyer and father of two.

Magnitsky had been an adviser to Hermitage, once the country’s biggest investment fund and now embroiled in a bitter legal battle with Russian authorities, while he worked at law firm Firestone Duncan.

“Doctors have a duty to treat people who are sick … and they simply did not treat him,” said Magnitsky’s brother-in-law. “In this way, they killed him, but I don’t know whether they did it intentionally.”

Relatives have said Magnitsky had suffered from stomach ailments since he was taken into prison almost a year ago.

Hermitage said in an e-mailed statement that prosecutors had rejected a request for an independent autopsy.

“The investigative committee of the Preobrazhensky Interregional Prosecutor’s Office of the city of Moscow refused to issue permission for a repeat autopsy,” the statement said.

Irina Dudukina, a spokeswoman for the Interior Ministry’s investigative committee, which announced the death, was not immediately available for comment after business hours.

Magnitsky’s mother and lawyers had requested the separate autopsy, Hermitage said in the statement.

“The relatives have well-grounded doubts about the objectivity” of an autopsy “supervised by the investigators and prison representatives who repeatedly refused to provide Sergei with medical assistance and drugs,” it said.

Justice Minister Alexander Konovalov said there was no evidence that a crime had been committed in Magnitsky’s treatment and challenged activists to provide facts to back their accusations, Interfax reported Thursday.

Magnitsky had been a suspect in a tax evasion case against Hermitage’s co-founder Bill Browder, a U.S. citizen who was refused entry to Russia in 2005 on national security grounds. Browder has accused the Interior Ministry of using Hermitage and other companies to fake tax refunds that have defrauded taxpayers of millions of dollars.

Magnitsky’s lawyer, Dmitry Kharitonov, said the official autopsy results, due in a month, should shed more light on the cause of death. He said Magnitsky was kept in prison too long and illegally.

“Unfortunately, this is normal in our country,” he said. “And his fingers were all smashed up. It was probably from banging on the [cell] door for help.”

Hermitage issued a statement Friday quoting Magnitsky as telling a Moscow court Nov. 12, four days before his death, that he had been chained and put in a cage.

“My right not to be subject to inhuman and degrading treatment, which undermines human dignity … has been violated,” he said.

Moscow prosecutors are looking into whether Magnitsky’s rights to medical treatment and decent living conditions were violated, the Prosecutor General’s Office said last week on its web site.

“We have filed complaints to all relevant agencies,” Kharitonov said. “We will monitor this probe and take steps depending on what decisions are made.”

(Reuters, Bloomberg)