Mr Kurumbliss first came to the attention of police a week after the murders, when the then 17-year-old boy said he found a bloody knife near the scene in Easy Street, Collingwood, an inner-city suburb.
The bodies of the school friends were found three days after they were last seen alive. Ms Armstrong’s one-year-old son was also found safe and sound in his cot at the house.
Both women suffered more than a dozen stab wounds and Ms. Armstrong was sexually assaulted, police said.
The case has long attracted enormous interest – it has become the subject of mass appeals by the police, true crime books and a hit podcast. In 2017, Victoria Police offered a reward of A$1 million (£511,800, $647,600) for information.
Commissioner Shane Patton described the killings as “absolutely horrific, horrific, insane murder” when he announced the arrest of Mr Kouroumblis – a Greek-Australian national – in September in Rome.
“This was a crime that struck at the very heart of our community — two women in their own home where they should have felt the safest,” he said.
Police have issued an Interpol red notice for Mr Kurumblis on two counts of murder and one count of rape since he left Australia about seven years ago.
But he could not be arrested in Greece, where he lived, because the country’s law requires murder charges to be filed within 20 years of the alleged crime.
At the time of Mr Kurumblis’ arrest, the women’s families released a statement saying their lives had been “irreversibly” changed by the murders.
“It has always been impossible for two quiet families from country Victoria to understand the senselessness and violence of Suzanne and Susan’s deaths,” the statement said.
Addressing the police, they said: “For always giving us hope and never giving up, we just say thank you.”