Three months before being stabbed to death in her Sydney apartment, Rita Caleo reportedly sent a sealed envelope to her solicitor.
The envelope read: "To be opened only if my death is unnatural.", Fairfax has reported today.
The contents of the envelope was opened by her solicitor in the presence of detectives following her murder in 1990.
She accused two people of organising the killing of her brother in gangland-style execution.
Mrs Caleo wrote in the letter that if she died an unnatural death, it would be the same people responsible for it.
This morning, more than 24 years since Caleo was stabbed to death in her apartment, a man has been arrested over her murder and is believed to be related to the family.
The homicide squad pounced on a 42-year-old man at Sydney International Airport after a flight from Kuala Lumpur landed shortly after 6am on Friday.
In the early hours of August 10, 1990, Rita Caleo, 39, and mother of two young children, was stabbed to death in her luxury Double Bay apartment in Sydney's eastern suburbs.
The man, who lives in Thailand and runs a restaurant in Phuket, was taken directly to Sydney Police Centre where he is expected to be charged with solicit to commit murder, accessory before the fact to murder, and accessory after the fact to murder.
"It's a very big arrest," Detective Inspector John Lehmann said.
A search warrant has been issued in Ramsgate, which will help gather further evidence, he said.
Further arrests are expected to be made.
The man was a teenager at the time of the brutal stabbing.
Mrs Caleo, a prominent businesswoman, was stabbed in the stomach in the ensuite of her bedroom while her two daughters, six months and four years old, were sleeping in the next bedroom.
Police said the live-in nanny heard noises from the main bedroom of the Bay St unit before discovering the body at 1.30am.
Mrs Caleo's husband, Mark Caleo, was working at one of his two Italian restaurants in Sydney at the time of the murder, police have said.
Det Insp Lehmann said on Friday that the murder of Mrs Caleo was made to look like a robbery.
"An intruder broke into the house and she was attacked in her bedroom," he said.
"It was an horrific murder."
Just 10 months before Mrs Caleo was murdered, her brother, Dr Michael Chye, was shot dead in his Mercedes-Benz in the garage of his Woollahra home.
Mrs Caleo's death happened just two days after a $50,000 reward was offered for information about the unsolved murder of her millionaire brother.
The siblings' father, Peter Chye, was a senior police officer in Malaysia and their deaths attracted significant public attention in Australia and Malaysia.
Police said on Friday that they believe a number of people were involved in the murders of Mrs Caleo and Dr Chye.
They wouldn't confirm if money was the motive but they do believe the two murders were connected.
The man is expected to appear at Central Local Court on Friday.
Morning news break – August 15