Mr Pereg initially reported the sisters missing, even posing for photos for news crews outside his home where he allegedly buried the two women.
He was arrested last week, prosecutor Claudia Rios said, after DNA on a t-shirt and a bag of cement allegedly tied him to the crime.
“Scientific staff found some apparently blood samples in a cement bag that was at the end of the property in a construction site,” she said.
Local media have reported the autopsy found nails hammered into both women’s bodies. One of the sisters was fatally shot three times, while the other showed signs of having been beaten and dragged.
A press release issued in Argentina on Monday said that further forensic testing is required to establish which sister is which.
“At the moment it has not been able to determine which body belongs to the woman Lily and which to Pirhya … in order to determine this, the corresponding DNA studies are being carried out, the results of which are awaited,” said the homicide investigators in a statement.
Next week the two women are expected to be repatriated to Israel, where they were born and where Ms Sarusi continued to live until her death.
Dr Pereg’s Australian partner is “devastated” by her death and not sleeping, friends say.
Dr Pereg had been living in Armidale since her appointment to the University of New England in 1999, moving there with her German ex-husband.
Several years ago she met a local man named John, who, friends say, is struggling to cope with the alleged murder of his partner.
“Poor devastated man. He is being so brave when his heart is shattered,” said friend Marg Duncan.
“Together they made a magic and special couple.”
“I know you have left a piece of your heart in Australia,” friend Tracy Adamson wrote in a Facebook post paying tribute to Dr Pereg.
Sally Rawsthorne is a Crime Reporter for The Sydney Morning Herald.