The man was arrested in Soweto on Saturday morning, Lieutenant Colonel Lungelo Dlamini said.
Lawrence Moepi was allegedly followed into the parking lot of the SizweNtsalubaGobodo offices in October, by men in a Volkswagen Golf. He was then shot allegedly by the 40-year-old and an accomplice, whilst he was getting out of his car.
The pair then allegedly fled the scene. The accomplice was still at large.
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.
It was reported that he had been appointed to work on the probe into the country’s multi-billion rand arms deal.
The arrested man was expected to appear in the Johannesburg Magistrate Court on Tuesday.