Christoff Becker, son of Hoërskool Waterkloof principal Dr Christo Becker, Frikkie du Preez, Gert van Schalkwyk and Reinach Tiedt are accused of assaulting a man in Constantia Park and killing another in Moreletta Park in late 2001.
All wrote matric last year at Hoërskool Waterkloof, except for Becker, who was at Hoërskool Garsfontein.
Earlier this week, State witness Heinrich von Landsberg was warned he would not receive indemnity from prosecution if his evidence was not honest and truthful.
His testimony was followed by that of a teenager, Witness A, who cannot be identified because of a court order.
Advocate Jaap Cilliers told Witness B, also a teenager, that if the four accused in a BMW had followed a running black man, as the boy had testified, it would have been between him and the claimed assault.
In any case, the four accused denied any assault had taken place.
Witness B said they had planned to drink coffee at a flat in Woodhill and he was driving his mother's Tazz in Constantia Park as he was looking for a cafe to buy milk.
Knew the youths from school
Witness B said he was 14 at the time of the alleged assault of a black man and the alleged murder of another black man in 2001.
He had gone to Hoërskool Waterkloof in the third term of 2001 and knew the four accused and Witness A from school.
Becker, Tiedt, Van Schalkwyk and another boy had been in Becker's father's BMW. and had spent time at a Hatfield club.
While looking for an open cafe, said Witness B, Du Preez ordered him to stop when he saw a black man sitting on the pavement.
Witness B said he saw Du Preez hit the man in the face.
Not long afterwards, there was a phone conversation with the BMW occupants and they met up with the Tazz.
The witness said they returned to where they had seen the man and Van Schalkwyk had chased and tackled him, followed by Tiedt, who trampled on the man's face.
The BMW then allegedly again sped away, leaving Tiedt behind to go in the Tazz.
The boys again met up at a park in Moreletta Park where the accused and Von Landsberg allegedly attacked and caused the death of another man.
'Man was rolling around and moaning'
"I remained behind with a girl in the Tazz when everyone ran into the park. They returned about 10 minutes later. I could not see what had happened," said Witness B.
At the Woodhill flat, three of the accused quarrelled, wondering what would happen if the man died.
The witness said they went back to the park to find knives and a hammer, as "Christoff was scared there might be fingerprints on it".
This time, Witness B also went into the park.
"I saw a black man rolling around and moaning. There was a stench of blood. I went back to the car and waited there," he said.
The trial will continue on November 29.