Police on Thursday said they had arrested two more people believed to be behind the killing of Mondeor High School pupil Kulani Mathebula.

This brought the number of suspects arrested to three.

"Police arrested two suspects early this morning, 14 March 2019, who are believed to be involved in the killing of the boy who was on his way to school yesterday (Wednesday) in Mondeor," said Captain Kay Makhubele.

The suspects, both aged 15, were arrested in Soweto and Naturena, he said.

The other suspect, a 13-year-old boy, was arrested in the Mondeor area on Wednesday afternoon.

Commenting on his arrest, Makhubele had said: "Police formed a team of detectives who followed up the information from the scene, which led them to another school in Mondeor, where one 13-year-old suspect attends."

Mathebula, 19, was fatally stabbed as he walked from home to school on Wednesday morning.

The incident happened at a park near his home, close to a police station.

It was not immediately clear whether anything was taken from him.

 At the scene, police and Gauteng education MEC Panyaza Lesufi had told the media that they believed three suspects were behind the killing.

CCTV footage captured from various cameras had led to the police expressing confidence that the three suspects would be soon arrested.