MOSCOW (AP) — Russian investigators are launching a criminal probe against two prison officials for their suspected role in the death of a jailed lawyer. But rights activists and the lawyer’s supporters accuse authorities of stopping short of naming the ultimate culprits in a case that has become a litmus test of President Dmitry Medvedev’s rule of law.

The Investigative Committee said in a statement Monday that a probe into the death of Sergey Magnitsky would focus on Larisa Litvinova, chief physician at the Butyrskaya prison in Moscow, and the prison’s deputy chief Dmitry Kratov. They are suspected of negligence that led to death.

Investors working in Russia, however, have raised concerns about the death and said it highlights corruption and inefficiency in the whole judicial system rather than of an individual case. The death has caused outrage in the Russian investment community and abroad.

Magnitsky was arrested by the same police officials he had accused of tax fraud.

Officials insisted in the past that the lawyer had died of heart failure. Monday’s announcement marks the first time a probe has been opened against anyone in the case.

Magnitsky died at Butyrskaya prison in November 2009 after the pancreatitis he developed there went untreated. He worked for Hermitage Capital Management, an investment fund owned and run by U.S.-born investor William Browder — since barred from Russia as a security risk.

Hermitage accuses Interior Ministry officers of seizing ownership documents of three of its subsidiaries in 2007, then using those documents to register their own people as owners. They then filed a tax claim, declaring a much smaller profit than originally reported and asked for a tax return, according to Hermitage.

The total return was 5.4 billion rubles ($230 million at the time).

Investigators said earlier this month that Magnitsky’s death resulted from a lack of medical help. But rights activists insisted that the probe should focus on investigators and police officers whom they suspect of giving orders to the doctors.

Magnitsky spent four of the last months of his life at Butyrskaya, during which time his family and supporters say he was never properly examined by a doctor. They say Kratov ignored Magnitsky’s pleas for medical assistance and surgery for three months.

He was, however, examined just hours before he died.

Browder told The Associated Press that the doctors were clearly following the investigators’ instructions in the case and "others higher up".

"The Russian government are desperately trying to create the appearance that they are doing something here, without going after the real guilty parties," he said.

Prominent human rights activist Svetlana Gannushkina told the Interfax news agency that investigators ought to open a probe not only into the negligence that caused the death, but also into torture: "I don’t believe that that (Magnitsky’s death) was an incidental oversight," she said.

Kratov and Litvinova are two of 60 Russian officials Browder and his supporters consider complicit in Magnitsky’s death.

Lawmakers in the Netherlands earlier this month voted in favor of a resolution demanding the government slap a travel ban on the officials. The U.S. Senate is working on similar legislation.