The director of forensic services at auditing firm SizweNtsalubaGobodo was shot dead at the company's office in Houghton, Johannesburg, on Friday morning, the company said.
The company named him as Lawrence Moepi, and said the firm would do everything in its power to aid the police's investigation into his killing.
According to a statement on the firm's website, Moepi had worked closely with the police's commercial crime unit and the now defunct Directorate of Special Operations, known as the Scorpions.
In his capacity as PricewaterhouseCoopers forensic services director Moepi testified in the fraud trial of former Scorpions official Geoffrey Ledwaba.
Constable Ndivhuwo Mulamu confirmed a man was shot dead in the area but could not immediately provide further details.
eNCA reported that Moepi was followed to his workplace by men in a VW Golf and shot dead as he got out of his car on Friday morning.
Police were investigating the motive as nothing was stolen from Moepi.
Business Day Live reported that he had been appointed to work on the probe into the country's multibillion-rand arms deal.
SizweNtsalubaGobodo executive chairperson Nonkululeko Gobodo praised Moepi.
"Lawrence was an inspirational leader and his insight, wisdom, and talent will be sorely missed," he said in a statement.
"Our thoughts and prayers go out to his family during this extremely difficult time." – Sapa