A report into the high-profile death of Russian lawyer Sergei Magnitsky says a senior investigator and a prison chief prevented him receiving medical care.
The report said there was reasonable suspicion that his death was triggered by beatings while in police custody.
The report, by a human rights council, was presented to President Dmitry Medvedev, who said it showed the death was probably criminal.
Magnitsky, who died in 2009, had accused officials of massive tax fraud.
No-one has been charged over the death of the 37-year-old lawyer or the tax fraud he alleged.
He was later accused of tax fraud himself, arrested and imprisoned without trial in November 2008, and died a year later, amid reports of terrible abuse in prison and denial of medical help.
His death sparked outrage among rights activists and was condemned by Western governments.
'Taken to room'
The interim report by the Human Rights Council of President Medvedev singled out senior interior ministry investigator Oleg Silchenko and prison chief Ivan Prokopenko as being at fault for neglect over the lawyer's death.
The document said they "obstructed" his medical care by moving him to another prison just before he was due to have an operation, where there was a criminal failure to provide him with care in the last days of his life.
This, it said, "can be seen as a deliberate worsening of his detention conditions and hindering of provision of medical care".
The council said that an hour before his death, Magnitsky had been taken to a small room by eight guards. There was no first aid provided.
"Before his death, Magnitsky was completely deprived of medical help. Additionally, there are grounds to suspect that Magnitsky's death was the result of a beating," the report said.
"His relatives afterward found that he had broken fingers and bruises on his body. Moreover, there is no medical record for the last hour of his life," it said.
Conflict of interest
And it pointed to a conflict of interest in the case, as some of those investigating Magnitsky were the very same people he had accused of massive corruption.
Earlier this year, Mr Medvedev promised a full inquiry into his death.
Responding to the report on Tuesday, he said: "A person has died, and it appears that there were crimes that led to that outcome."
"Magnitsky's case is a very sad one," he said. "Ailing people shouldn't die in prison. If they fall ill, they must be taken out for treatment before a court decides their fate."
He said the report would be handed to investigators for further action.
Magnitsky was a lawyer for a large US investment fund operating in Russia, Hermitage Capital, that Russian officials say evaded paying taxes.
Hermitage boss William Browder accuses Russian officials of using his company to operate a $230m (£143m) tax fraud.
Magnitsky claimed to have unearthed evidence that implicated the police, officials and bankers in the fraud.