By Steven Eke
BBC Russian affairs analyst
Deaths in custody are not uncommon in Russia
The death in prison of a Russian lawyer has sparked bitter accusations of maltreatment of inmates.
Sergei Magnitsky, 37, who was being held on suspicion of conspiracy, died this week from what investigators say was acute heart failure.
It has since emerged he had repeatedly complained about prison authorities' refusal to allow him medical care.
Mr Magnitsky had acted for Hermitage Capital Management, once a leading foreign investor.
A spokeswoman for the Russian prosecutor's office says Mr Magnitsky's death was tragic and came as an absolute surprise.
She acknowledged that he had complained about prison conditions, which are often overcrowded and extremely unhygienic in Russia.
A statement from Hermitage said that he had also complained about being denied treatment for digestive problems.
Deaths in custody, sometimes involving ill-treatment, are not uncommon in Russia.
But Mr Magnitsky's role in defending Hermitage means that the case has drawn wider attention and immediate comment.
The leading Russian business daily, Vedomosti, has said the authorities were responsible for what it called a "medieval death".
Meanwhile, a colleague from Mr Magnitsky's former Moscow legal practice said it showed there was no law in Russia.
Mr Magnitsky was arrested on suspicion of conspiracy after agreeing to defend Hermitage against alleged tax evasion.
Hermitage, the brainchild of US businessman William Browder, was one of the largest investment funds in Russia from the mid-1990s.
But in 2005 Mr Browder was banned from Russia as a threat to national security.
That was after Hermitage had gone public with accusations of large-scale corruption in state corporations.
Mr Browder says he was punished for being a threat to corrupt politicians and bureaucrats.
Since then, a number of Mr Browder's associates in Russia - as well as lawyers acting for his company - have been detained, beaten or robbed.
Lawyer Sergei Magnitsky is the first person involved in the case to have died.