Police have accused her husband, Shrien, of hiring a team of hit men to kill 28-year-old Anni, while holidaying in Cape Town in November 2010.
However, the 33-year-old Bristol-based businessman, fighting against his extradition from UK to South Africa, has always maintained that he was forced from a taxi by carjackers who drove off with his wife and killed her.
But a new British Broadcasting Corporation documentary, to be telecast on Thursday, cast doubts over his involvement, based on fresh ballistic evidence and CCTV footage.
According to the Sunday Telegraph, Anni's uncle, Ashok Hindocha, has written to BBC director-general Lord Hall about the family's concerns and accused the corporation of acting callously and insensitively.
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"The murder of Mrs Dewani has caused us great grief and pain. Not a day goes by without us remembering and crying for her. Her mother has cancer and hardly leaves the bed. We cannot see why you are broadcasting a second programme," the letter states.
The BBC programme is expected to raise doubts over the police case against Shrien, after obtaining what it describes as "secret police files".
It is understood that the channel commissioned a forensic examination of the case, including asking a pathologist to examine material from the police file and has asked South African police to respond to criticisms levelled at it by the experts.
Publicity material for the programme said, "Their findings expose fundamental mistakes both in the police investigation and in the interpretation of forensic evidence."
"We received replies from Mr Hindocha which did not raise these objections. Should the Hindocha family wish to issue a statement then we would reflect their position in the programme," he added.