Nearly two years after her son died in custody, a slight, 59-year-old retired teacher is confronting the powerful officials who put him in prison and oversaw the system that has been blamed for his death.

Natalya Magnitskaya has avoided public attention since her only child, Sergei L. Magnitsky, died in pre-trial detention. Working for an American law firm in Moscow, he had uncovered a $230 million tax fraud and accused police of the crime. The very officers he testified against soon arrested him and charged him with the fraud.

His mother was sure the truth would quickly come out, and he would be freed. He was young, healthy and confident, and 11 months later he was dead.

Now, despairing that those who caused his death will ever be prosecuted, Natalya Magnitskaya has filed an official complaint with Russia’s Investigative Committee, asking for a murder investigation of Russia’s chief prosecutor, deputy interior minister and other police, security and prison officials.

Newly discovered documents accompany her complaint: Three days after Magnitsky died, in November 2009, an investigator filed a report saying the evidence warranted opening a murder case. That report was never publicly disclosed, and a week later, as the death raised concerns around the world, the authorities began investigating negligence instead of homicide.

The complaint, accompanied by photos of his injured wrists and hands, asserts that Magnitsky was beaten by eight officers with rubber batons in the last hour of his life, an allegation that has not been investigated even though it was raised by a presidential commission.

“I didn’t understand the scale of the corruption,” his mother said in an interview last week.

Magnitsky’s agonizing death at the age of 37 — he had developed pancreatitis and gallstones in prison that went untreated even though a doctor ordered surgery--- has become an international incident, setting off a legislative assault against Russia in the U.S. Congress, threats of sanctions from European leaders and the probe ordered by President Dmitry Medvedev, which found the charges against Magnitsky had been fabricated and his confinement tantamount to torture.

With Russian officials under intense pressure to explain why and how Magnitsky died---the cause was reported as heart failure---two prison doctors recently were charged with negligence.

“Not only doctors are to blame,” his mother said, “but only doctors have been accused.”

Her lawyers have been steadily peppering the Investigative Committee and other agencies with requests for information about Sergei’s death. They have been unable to see prison records—on the grounds that none of his rights had been violated---and have been refused access to investigations that cleared police personnel of any connection to the death. Neither have they been able to have experts review medical records and tissue samples. On Friday, the committee said it could not immediately say what had happened to Magnitskaya’s new complaint.

Her lawyer, Nikolai Gorokhov, said that complaint was necessary because it was clear no serious investigation into Magnitsky’s death was being pursued.

“These individuals are stealing huge amounts of money,” he said. “Of course they don’t want an investigation.We do have concerns about bringing a complaint, but if we don’t do it, who will?”

In the United States, the State Department has put a number of Russian officials connected to the case on a visa blacklist. Last month, Sen. Ben Cardin (D-Md.) wrote an opinion piece in The Washington Post, calling Magnitsky a hero and explaining why he had sponsored a law in his honor that would require sanctions against Russians who violated human rights.

“He was denied medical care and beaten by prison guards; he died alone in November 2009 in an isolation cell as doctors waited outside his door,” Cardin wrote. “These facts are accepted at the highest levels of Russia’s government, yet those implicated in his death remain unpunished, in positions of authority. Some have even been decorated and promoted.”

Earlier this month, the Interior Ministry summoned Natalya Magnitskaya for questioning. They have reopened the investigation of tax fraud charges against her son, which had been closed when he died. She has refused to appear.

“I’m not frightened for myself,” she said last week, her voice quiet and hesitant. Nothing, she said, can be worse than losing her son.

Magnitskaya described him as one of the country’s best and brightest. A child who loved to read, he had grown up in the small town of Nalchik, in the foothills of the Caucasus Mountains, always getting 5’s---straight A’s in Russia.

In 1991, as the Soviet Union dissolved and Russia set out toward independence, Magnitsky was 19, studying economics at the Plekhanov Academy in Moscow. Those were difficult years. At one point his mother lost her job, and his parents—his father is a retired engineer--- had a hard time buying food. This, at last, makes his mother smile, remembering how she sent him potatoes from a thousand miles away because she worried that he wasn’t getting enough to eat. He earned a Red Diploma, an honors degree.

“He loved his job,” she said. “He believed life would be good in this country. He believed you could live and work here, and the law would protect you. Maybe he was naïve, an idealist, but he was always honest.”