Mr Kouroumblis first came to police attention the week after the murders, when the then 17-year-old said he had found a bloodied knife near the scene in Easey Street, Collingwood, an inner-city suburb.

The bodies of the high school friends were discovered three days after they were last seen alive. Ms Armstrong’s one-year-old son was also found in the home, unharmed in his cot.

Both women had been stabbed more than a dozen times and Ms Armstrong had been sexually assaulted, police say.

The case has long drawn huge interest – becoming the subject of major police appeals, true crime books and a hit podcast. In 2017 Victoria Police offered a A$1m (£511,800, $647,600) reward for information.

Commissioner Shane Patton described the murders as “an absolutely gruesome, horrific, frenzied homicide” when announcing the arrest of Mr Kouroumblis – a dual Greek-Australian citizen – in Rome in September.

“This was a crime that struck at the heart of our community – two women in their own home, where they should have felt their safest,” he said.

Police had issued an Interpol red notice for Mr Kouroumblis on two charges of murder and one of rape, after he left Australia about seven years ago.

But he was not able to be arrested in Greece, where he had been living, as the country’s law requires murder charges to be laid within 20 years of an alleged crime.

At the time of Mr Kouroumblis’s arrest, the women’s families released a statement, saying their lives had been changed “irrevocably” by the murders.

“For two quiet families from country Victoria it has always been impossible to comprehend the needless and violent manner in which Suzanne and Susan died,” the statement read.

Addressing police, they said: “For always giving us hope and never giving up, we simply say, thank you.”