Former Independent Police Investigative Directorate (Ipid) head Robert McBride is testifying at the state capture inquiry.
McBride is set to give evidence on the role of the police in aiding and covering up state capture.
He was initially set to testify in February, while he was still the executive director of Ipid. However, parliament’s police committee has since endorsed the decision by police minister Bheki Cele not to renew McBride’s contract.
In September last year, the Sunday Times reported on new claims about a mysterious Russian-trained police death squad that may have been involved in political assassinations, break-ins and harassment during the Zuma presidency.
McBride is expected to tell the commission he was investigating the whereabouts and activities of the squad, which was trained in "offensive warfare". This included sniper training, the use of rocket launchers and ambushes.
McBride told the Sunday Times that in late 2016, 16 men were hired on the pretext of guarding offices of the Hawks, but were sent for specialist training to Russia. Weapons training might also have been conducted in China, he said.