Three months before she was stabbed to death in her Double Bay apartment, Sydney restaurateur Rita Caleo gave a sealed envelope to her solicitor.
The envelope read: "To be opened only if my death is unnatural."
Inside the envelope, which Mrs Caleo's solicitor opened in the presence of detectives following her murder in 1990, were the names of two people she accused of organising the gangland-style execution of her brother, a wealthy doctor, at his Woollahra mansion the previous year.
If she died an unnatural death, the same people would be responsible, Mrs Caleo wrote in the letter.
On Friday morning, more than 24 years after Mrs Caleo was stabbed to death in her bedroom ensuite, homicide squad detectives arrested a man at Sydney International Airport in what they described as a "major breakthrough" in the case.
Gerard Caleo, a 42-year-old Australian who lives in Thailand and runs the Hard Rock Cafe in Phuket, was arrested by Homicide Squad detectives after landing in Sydney on a flight from Kuala Lumpur just after 6am.
It's believed he is the brother of Mrs Caleo's husband.
Detectives from the Unsolved Homicide Team have charged him with solicit to commit murder, accessory before the fact to murder, and accessory after the fact to murder.
Mrs Caleo, 39, was stabbed in the stomach during the night of August 10, 1990, while her two children were asleep in an adjoining bedroom.
A live-in nanny heard muffled sounds coming from the main bedroom of the unit in Bay Street before finding Mrs Caleo's body at 1.30am.
Her husband, Mark Caleo, was working at one of his two Sydney Italian restaurants at the time of the killing, police said at the time.
Detective Inspector John Lehmann, from the Unsolved Homicide Team, said her killing 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."
Mrs Caleo's death came less than a year after her brother, millionaire Sydney doctor Michael Chye, was shot dead as he drove his Mercedes into the garage of his mansion at Attunga Street, Woollahra.
That killer apparently escaped through the automatic roller garage door within the 10 seconds it took for it to open and close on the night of October 17, 1989.
An inquest into his death in 1991 found that Dr Chye, his sister and her husband had been been involved in a dispute over a $3.6 million waterfront property in Blakehurst, in southern Sydney.
Dr Chye had also been questioned in 1989 by members of the Hong Kong Independent Commission Against Corruption in relation to a multimillion-dollar fraud involving a Hong Kong bank. However, police at the time told the inquest into his death that they did not believe this was related to his murder.
Detective Inspector Lehmann said on Friday that police believed the same people were responsible for both deaths.
"We do think that both the murders are linked. Rita Caleo was murdered some 10 months after the murder of Dr Michael Chye, and yes ... we do believe that the same persons are responsible," he said.
“We know there are a number of people who were involved in Mrs Caleo and Dr Chye’s deaths and we are hoping to make more arrests in the future.
“My advice to anyone who was involved in these incidents, even if only by association, is to contact us before we come to you.”
The inquest into Mrs Caleo's death in 1991 heard that she had handed her solicitor the sealed envelope just three months before her own death.
However the coroner, Kevin Waller, said at the time that the evidence failed to establish a prima facie case against any known person.
Despite extensive investigations into both murders during the 1990s, no one was charged over the siblings' deaths.
Mrs Caleo and Dr Chye’s father, Mr Peter Chye, was a senior-ranking police officer in Malaysia and their deaths attracted widespread coverage in both Australia and Malaysia.
The NSW Police Force’s Unsolved Homicide Team took over of the investigations under Strike Force Nichola in 2008.