A 19-year-old Queensland woman has been arrested over the "shocking" suspected murder of her 81-year-old grandfather in his home north of Adelaide earlier this month.
Brittany Jade Dwyer and her 21-year-old friend Bernadette Burns, both from Redbank Plains, are scheduled to appear in the Brisbane Magistrate's Court tomorrow, where South Australian police will apply for their extradition.
It is expected they will then be formally charged with the murder of Robert Whitwell, who was found dead in his Craigmore home on August 8.
SA police have described the scene inside Mr Whitwell's house as "very unusual".
"The circumstances surrounding the murder are quite shocking," Detective Inspector Greg Hutchins said yesterday.
"It was one of those scenes that was very difficult to read."
Det. Insp. Hutchins said investigators initially believed the 81-year-old had likely died of natural causes but there were a number of factors which couldn't be explained.
It took a team of forensic investigators and crime scene pathologists to work out what had occurred inside the house.
After it was determined Mr Whitwell had likely been murdered, officers flew to Queensland and conducted interviews and searched properties on Friday, Det. Insp. Hutchins said.
Mr Whitwell's granddaughter and her friend were subsequently arrested, and no further arrests are anticipated.
Det. Insp. Hutchins said Mr Whitwell's family was "devastated".
With AAP.