Dewani is accused of orchestrating the murder of his bride Anni Dewani during their honeymoon in Cape Town in 2010.
Anni, a Swedish national, was shot outside the city, in what appeared like a botched hijacking.
The BBC's Panorama claimed that privately conducted ballistic evidence suggested that the shooting was an accident.
Professor Jim Fraser told the BBC's Panorama programme there was "simply a cloud of suspicion... rather than any evidence" against Dewani.
It also alleged state evidence might be flawed, in a high-profile case that has led to protracted legal wrangling between the two countries.
Dewani remains in Britain in a mental health clinic where he is being treated for post-traumatic stress disorder and is fighting extradition to South Africa.
"The matter is sub judice. We don't want to have the trial discussed in media," the National Prosecuting Authority (NPA) spokesperson Eric Ntabazalila said.
"We have faith in the work done by our police."
Firearms experts at the Forensic Firearms Consultancy in London are said to have been commissioned to review the evidence.
Ntabazalila expressed concern at how the broadcaster got access to crucial files containing evidence.
"All I know is that the broadcaster approached us earlier this month for our view on the findings and we declined to take part," Ntabazalila told AFP.
"That would have undermined his right to a fair trial," he added.
Three local men, including their driver on the day, have been jailed over the killing. They claimed that Dewani ordered the hit.
Dewani denies any involvement.
He was arrested in Britain in 2010 for the murder and released on bail.
British authorities have recently ordered that the Bristol-based 33-year-old be tried in South Africa, ending a lengthy legal challenge.
His lawyers have argued that he was suffering from serious mental illness and that the country's crowded and often violent jails were not good for his health.