The man reportedly lived in Greece, where he was protected by the country’s statute of limitations, according to Australian media.
Australian police said on Saturday they would start the process of extraditing the suspect, and Italian courts would set the timeline.
The suspect is accused of killing two friends — Suzanne Armstrong, 27, and Susan Bartlett, 28 — in a knife attack that shocked Australia in January 1977.
The young women were found dead in their rented house on Easey Street in Melbourne, while Armstrong’s 16-month-old son was left unharmed in his cot in another room. Both Armstrong and Bartlett had been stabbed multiple times.
The crime, known as the “Easey Street murders,” became Melbourne’s longest and most serious cold case, but no one had been arrested until now.
Victoria Police offered a $1 million reward in 2017 to catch those responsible. That same year, new technology led to a breakthrough in the case, as the suspect became a fugitive following a request for a sample of his DNA.