Nkwalase said the suspects fled with cash after locking both guards in the ATM vault‚ leaving the assault rifle outside.
All the while the unsuspecting driver of the armoured cash van waited in vain for his colleagues to finish their delivery.
Nkwalase said more arrests were expected. The suspect will appear in Stellenbosch Magistrate's Court on Monday.
The breakthrough is a welcome success in a week which saw a highly organised and brazen attack on a cash-in-transit convoy in Boksburg in Ekurhuleni.
In that heist‚ 10 men in luxury cars and armed with assault rifles attacked two vehicles and used explosives to blow the armoured skins off the trucks.