The family of Australian scientist Lily Pereg, whose remains were discovered in Argentina, have expressed their shock and sadness after her nephew was charged with her murder.

The body of Ms Pereg, a 54-year-old Israeli-born microbiology professor at the University of New England (UNE) was found in a shallow grave on Sunday near the city of Mendoza alongside that of her 63-year-old sister Pirhya Sarussi. 

The bodies were buried on a lot beside the house of Ms Sarussi’s son Gilad Pereg, 36, who has been formally charged with the aggravated homicide of his mother and the simple homicide of his aunt, according to Argentine prosecutor Claudia Rios.

No motive for the alleged murder has been revealed.

After news of the discovery of the women’s bodies and the arrest of Gilad Pereg, their family revealed how Ms Pereg “weirdly” stopped replying to daily messages from her friends about two weeks before she was found dead.

“We the family, are shocked. Gilad Pereg, Pyrchia Sarusi’s son, standing accused of murdering his Mother and Aunt [sic],” the family said in a statement on a GoFundMe set up to raise funds to help find the women.

“We are … humbled by the outpouring of support and love, worldwide,” the statement said.

“Your love carried us and will help us recover from a huge tragedy. There will never be an explanation.”

Gilad Pereg is in custody, charged with the women’s murder.

The family had collected more than $7500 in donations to help find the women. The funds will now be donated to charity.

The pair vanished around January 11 after travelling to Mendoza to visit Gilad, who had been living in Argentina for more than 10 years.

Childhood friend Eti Krief Haimi said she was in daily contact with Ms Pereg via a WhatsApp group chat called “friendship forever”.

“The last message you sent to us on 11/1/19 hour 23.06 was: ‘wishing you a peaceful Shabbat.. Shabbat shalom dear girls..’ with full of hearts and flowers,” she posted on Facebook.

“You stopped responding to us, it was a little weird, but we thought you were on a flight somewhere.”

Ms Haimi paid tribute to Ms Pereg’s “big smile” and love of life and travel.

“You left a huge hole with us. We didn’t dream in the worst deal we’d have to break up with you so fast.”

Autopsy results showed at least one of the women was shot. Local media are reporting the victim had suffered three gunshot wounds while the other showed signs of having been dragged.

Lily Pereg and her sister Pirhya Sarusi were found in a shallow grave.

Gilad Pereg, who reportedly was the Argentine chairman of five companies set up by his mother, has been transferred to a local prison.

The Department of Foreign Affairs and Trade on Monday confirmed it was providing consular assistance to the family of an Australian woman who died in Argentina.

“Owing to our privacy obligations we will not provide further comment,” a spokeswoman said.

The UNE website describes Dr Pereg as a microbial ecologist with 25 years’ experience as a researcher in plant and social microbiology.

She obtained a PhD from the University of Sydney in 1998 and later worked for the Institute for Genetics at the University of Cologne in Germany before joining UNE in 2001.

The university has been contacted for comment. 

-with AAP