South Australian police have charged an 18-year-old man with the murders of a Kapunda couple and their 16-year-old daughter last week.

Locals had been traumatised by the killings of Andrew, Rose and Chantelle Rowe, who were repeatedly stabbed in their Harriet Street home.

A large crowd gathered outside the Kapunda police station once news spread that a man had been arrested.

Although police held a press conference, they did not release details of how they came to arrest the man.

Police will not publicly identify him, but it is believed the man was known to Chantelle Rowe and played on a local basketball team.

He will appear in the Elizabeth Magistrates Court today.

Police have thanked the community for assisting the investigation.

One local says she is worried there could be a backlash against the family of the accused.

The Rowe family had moved to the house just months ago from another property in Kapunda, which is 76 kilometres from Adelaide.

Police revealed on Monday they had obtained a DNA profile of an unknown man from the crime scene.

They were also looking for the owner of a white Toyota Landcruiser tray top seen outside the home.

The Rowes' son, Christopher, was holidaying on the Gold Coast when told of the deaths. He is being comforted by family and friends.

The back gate of the family's property has become a small shrine of flowers, tribute messages and teddy bears.