A man arrested over the horrific cold-case killings of two Melbourne women was known to be in Greece, but investigators had to wait for him to leave the country before they could swoop.
Suzanne Armstrong, 28, and Susan Bartlett, 27, were found dead with multiple stab wounds in their home on Easey Street in Collingwood in January 1977.
Ms Bartlett's 16-month-old son Gregory was found unharmed in his cot.
On Saturday, it was revealed a 65-year-old man had been arrested at Leonardo Da Vinci Airport, in the Italian capital Rome, over the slayings which came to be known as the "Easey Street murders".
Victoria Police Chief Commissioner Shane Patton said the force had put out an INTERPOL red notice alert for the dual Australian-Greek citizen on two charges of murder and one of rape.
Mr Patton said the man had been one of many people of interest in the case and investigators had been "looking for him for a number of years", but had to wait for him to leave Greece.
"He wasn't able to be arrested in Greece. There is a 20-year, as I understand, statute bar on initiation of murder charges (in Greece)," he told reporters on Saturday.
"Our warrant wasn't issued within that 20-year period."
It's unclear why the man was in Rome, but he remains there in custody as Australia starts the legal process to bring him back.
Mr Patton described the murders as "an absolutely gruesome, horrific, frenzied homicide".
He said advances in technology, investigative techniques and retracing statements had contributed to the breakthrough.
"This is Victoria's most serious cold case and longest cold case that we have ever solved, and that's why it is such a significant achievement," Mr Patton said.
"There is simply no expiry date on crimes that are as brutal as this"
The two friends were last seen alive on January 10, 1977, and their bodies were found three days later.
Their deaths shocked Australia, but no one has been arrested until now.
Victoria Police offered a $1 million reward in 2017 to catch those responsible.
The women's families said it was difficult to express their level of appreciation to investigators who tirelessly pursued answers and justice for so long.
"The perseverance and dedication required to achieve the result today is something to truly behold," they said in a statement on Saturday.
"For always giving us hope and never giving up, we simply say, thank you."
The women attended school together in Benalla, in Victoria's high country, and their families said their deaths changed many lives "irrevocably".
"We will be forever grateful for the support and understanding shown to us by our friends and family over the past 47 years," they said.
Mr Patton described the arrest as an important breakthrough but warned it was "just the start of the journey" as the investigation continued.
He said the federal attorney-general would start the process of extraditing the man and Italian courts would set the timeline, but he doesn't expect Australian law enforcement to go over to Italy for at least a month.
