Owner Barry Newman was duped into letting his killers into the home near Johannesburg on 28 September (12) when they claimed they were interested in buying his girlfriend's used car. Once inside, they turned on him and tied him up in the bathroom.
The victim was also allegedly burned by a hot clothing iron and lit cigarette and suffocated with a plastic bag.
A gardener and domestic worker were also found locked inside the house.
Law enforcement officials have launched a full investigation into the incident, but no arrests have been made.
This isn't the first murder to occur at the residence - the Monster star's mum Gerda shot and killed Theron's alcoholic and abusive dad Charles 21 years ago.
Gerda claimed self-defence and authorities declined to press charges.