A "drunk and highly emotional" teen broke several knives in fatally stabbing 18 times the grandmother who raised him in a frenzied attack in her Sydney home, police allege.
Ethan Harwood, 19, then tried to set fire to her house while a television played a DVD of him and the woman on holidays in Hawaii in 2012, they say.
Harwood faced Melbourne Magistrates Court on Friday as NSW police detectives applied to have him extradited to Sydney.
He is accused of stabbing to death 67-year-old Pauline Farrugia at her Penrith South home on Saturday.
Police found Ms Farrugia's body next to several broken knives on Wednesday after one of her daughters reported her missing.
Harwood had lived with Ms Farrugia for most of his life, according to a NSW police summary.
She raised him until he went to live with his mother at Nhill in western Victoria about a year ago.
Police allege Harwood became drunk and upset at a barbecue with his sister and other relatives on the day of the murder.
"The accused became well intoxicated and emotional," police say.
Other people overheard him telling his mother on the phone that he "wished he had never been born" and complaining of being physically abused by his grandmother when he was a child.
Police allege Harwood abruptly left the barbecue and went to his grandmother's house while in a "highly emotional state".
"Whilst inside the house, the accused attacked the deceased, inflicting at least 18 stab wounds to the torso of the deceased using several knives," police say.
"The attack appears to be uncontrolled and the accused broke several knives while attacking the deceased."
Harwood then allegedly tried to set fire to his grandmother's house.
The stove and oven had been turned on, a smoke alarm was removed, and a woman's wallet had been set alight using matches, police say.
The TV near Ms Farrugia's body had also been switched on.
"Oddly, the television showing a DVD of the accused and the deceased on holidays in Hawaii in 2012," police noted.
It's alleged the teenager ransacked the home before stealing Ms Farrugia's car.
After her body was discovered, police found her unlocked car at Penrith railway station with the key still in the ignition and a knife on the passenger seat.
CCTV footage shows a barefoot Harwood entering the station at 12.20am on Sunday, according to the police summary.
Police allege a pair of black shoes found at Ms Farrugia's house belong to her grandson.
Harwood was arrested at his mother's Nhill home on Thursday.
Outside court on Friday she told media "my son is innocent".
The teenager is due to arrive back in Sydney on Friday evening and will face Parramatta Local Court on Saturday.