Two people were shot dead during the robbery. One person was wounded while two were arrested on Thursday.
"[Meanwhile] another man [believed to have been a robber who fled and was] hiding in Edenvale was arrested on Friday," said Makhubele.
The robbers allegedly gained entry to the school after one of them told a security guard he had come to pick up a learner.
"While security guards were opening for him, more armed suspects entered, driving a van. It is alleged that the suspects proceeded to the offices where they held the principal at gunpoint and robbed him of an undisclosed amount of cash," said Makhubele.
Police rushed to the scene where a shootout ensued.
Makhubele said one of those arrested was in one of two getaway vehicles that the group used to flee the scene.
The car was found a street away containing an R5 rifle and a pistol.
"A total of five firearms were recovered by the police, one AK47,one R5 and three pistols," said Makhubele.