Thirty-six awaiting trial prisoners were being transported from Randburg Magistrate's Court to the Johannesburg Correctional Services Facility in Naturena, south of Johannesburg, when a bomb exploded at the back of the police truck. Fifteen prisoners were injured.
A case of murder, possession of explosives and escape from lawful custody is being investigated.
According to the police, the driver heard a loud bang when he reached the corner of Naturena and the old Soweto Highway. He immediately noticed a hole in the rear door of the truck. Two prisoners were trying to flee. They were captured before the truck drove to the correctional service facility for safety reasons, said the police.
"All evidence at the scene has been collected and was sent to a forensic lab for analysis. Investigators are busy tracing and locating the next of kin of the deceased," said police spokesperson Brigadier Neville Malila.
Because the prisoners died while in police custody, the investigations will be led by the Independent Police Investigative Directorate (IPID) with the help of the police. "We have assigned a team of investigators to assist the IPID," Malila told the Mail & Guardian.
Malila said the investigation is in its early stages and statements are being taken from the prisoners.
In reaction to Monday's blast the South African Prisoners' Organisation for Human Rights (SAPOHR) said it holds the police, the justice department and the department of correctional services "accountable for their negligence".
SAPOHR president Golden Miles Bhudu said he believes the explosives were smuggled in at one of the three institutions.
"How can a bomb be smuggled from the court and taken to the holding cells and then into a police vehicle? But we are not surprised, you can smuggle anything in our courts and prison cells, there is no security. The department of correctional services, the police and the justice system should apologise to the bereaved families … They should also be compensated because of states negligence," said Bhudu.
"The judiciary should be sued and dragged screaming to the court to for what has happened," Bhudu told the Mail & Guardian.
SAPOHR plans to approach the Wits Law Clinic, the Lawyers for Human Rights and the Legal Resources Centre to advise those affected about their legal rights in the case.