Dr Raghavjee, 60, was carjacked and shot dead for no apparent reason during his drive to work in the Eastern Cape town of Port Elizabeth.
His widow Heather travelled to Cape Town to support Shrien Dewani when he and his new wife were carjacked and she was shot dead last month.
Police, who allege that Mr Dewani arranged a fake carjacking to have his wife killed, later suggested that there could be a link with the death of Mr Raghavjee because the families knew each other, and sent detectives from the capital Pretoria to investigate.
But Christian Botha, a private investigator based in the Eastern Cape commissioned by Mrs Raghavjee in June to look at her husband's murder again, said he was executed because he was about to disclose incriminating information.