A man who stabbed an elderly couple to death wanted to know what it felt like to kill, a court has heard.
The double murder of an elderly Melbourne couple was nothing more than a thrill kill, a judge has said.
Thomas James Hemming, 21, held lifelong fantasies about what it would feel like to kill, the Victorian Supreme Court heard.
In the early hours of February 19, the Murrumbeena man acted on them.
He put on black gloves and a black leather jacket and stuck a knife he had ordered online in a scabbard.
At 6am he knocked on the door of neighbours Robert Adamson, 65, and his wife Cheryl, 60, telling them he needed to use their phone.
Once inside he stabbed Mr Adamson in the back and chest multiple times, the court heard.
Mrs Adamson picked up a broom and swung it at Hemming before he turned his attention to her.
Prosecutor Gavin Silbert SC said Hemming told police he thought it was better to kill an old couple than someone young.
"He wanted to know what it felt like to kill someone," Mr Silbert told the pre-sentence hearing on Monday.
During his police interview Hemming initially denied his involvement in the Adamsons' deaths but he has since pleaded guilty to two counts of murder.
Defence lawyer Damian Sheales said Hemming was a youthful offender who had lived a narrow existence and had Asperger's syndrome.
Justice Betty King described the murder as a "thrill kill".
"It's terrifying," Justice King said.
"There's just no feeling. No empathy. No care."
Psychologist Daniel Sullivan said Hemming had a preoccupation with killing.
People with Asperger's syndrome are more likely to be victims of violence, than violent offenders, Dr Sullivan told the court.
A friend of the Adamsons, Andrew Masters, said the crime is scarier now that he knows there was no real motive.
"There was some suggestion that Asperger's limited his ability to feel for the victims, but I have Asperger's myself and I feel plenty for the victims," he told reporters outside court.
Hemming, who lived 160 metres from the Adamsons, will be sentenced on a date to be fixed.