The Independent Police Investigative Directorate on Tuesday said it began taking statements from witnesses after a prisoner was apparently killed by police.
The incident occurred over the weekend when several inmates tried to escape at Lansdowne Police Station in Cape Town.
It is believed a police officer was overpowered by one of the men when he visited their cell.
An inmate was shot dead and another was wounded.
Three of them were re-arrested shortly after the incident.
The directorate's Moses Dlamini said the matter is receiving their attention.
“We’ve interviewed different people. Police as well as suspects who were witnesses to the whole incident. The investigation is still underway and is at early stages.”
Meanwhile, police said the 26-year old fugitive arrested in connection with Sunday’s escape from the cells is wanted in connection with a string of other offences.
Ighsaan Dyers was part of a group that fled, after overpowering a police officer.
Police assembled a team of detectives from the Lansdowne Police Station to track him down and he was arrested on Monday.
The police's Frederick van Wyk said, "They arrested him in the Manenberg area and he will appear in court once he has been charged."
(Edited by Lisa Bartlett)