The first Russian official charged in the death of Sergei Magnitsky, a lawyer who died in prison after reporting a multimillion-dollar tax fraud, went on trial Thursday and pleaded not guilty.

Dmitry Kratov, formerly a doctor in Moscow's Butyrka prison, was charged with negligence.

Kratov's attorney, Roman Kuchin, said his client denied the charges because he was not able to ensure medical care for Magnitsky in prison due to a shortage of staff.

Magnitsky, who in 2007 who had accused Interior Ministry officials of using false tax documents to steal $230 million from the state, died in custody from untreated pancreatitis in 2009. An investigation by Russia's presidential council on human rights concluded that Magnitsky was severely beaten and denied medical treatment. It accused the government of failing to prosecute those responsible.

Magnitsky's relatives and colleagues say by charging the prison doctors, authorities are trying to cover up for the police officers and the investigators who denied Magnitsky's pleas to be released. The lawyer died before he was brought to trial.

Nikolai Gorokhov, a lawyer representing Magnitsky's mother, said Kratov was guilty "because the absence of medical help, which inevitably caused the death of that person, is a premeditated crime."