Johannesburg - She begged the robber not to kill her husband, but while she was watching, the armed man stabbed Corrie Muller, 81, in the throat. Hettie, 78, watched him bleed to death.
Corrie was killed in Germiston at about 08:30 on his granddaughter's birthday on Wednesday.
Son-in-law Marius Mills said the robber broke down the burglar bars in the kitchen to gain entry to the house. He then punched Hettie in the face and threw cups at her. He told her he would bite off her finger if she didn't give him her wedding ring.
She screamed and Corrie, who was in the shower, came to her aid. The men fought and the robber then got hold of a kitchen knife.
Hettie apparently begged the robber not to kill her husband, but the man stabbed Corrie in the throat, severing a main artery. The man stole Corrie's cap and cellphone.
A 17-year-old youth was later arrested after the cellphone was found in his possession. Two others, who were also arrested on Thursday, showed out the teen's hiding place to police.
They were part of a gang of five who apparently admitted coming to Primrose to rob homes. Four of the five were later arrested.