An autopsy two days later found 15 separate lacerations and extensive facial fractures.
Before leaving the address, the teen placed towels on the stove and turned it on.
As it smouldered, he packed a bag with underwear, a T-shirt, shorts and a bottle of water and fled on foot.
In Fea St, North Dunedin, 4km away, the defendant knocked on a door and asked the residents if he could use a phone.
The court heard he spent 26 minutes on a call to police, at first describing “an assault” but reluctant to give detail.
“During that phone call, the defendant sounded lucid and coherent, but at some stages sounded upset and crying,” a summary of facts said.
He provided his name and his home address, where the killing had taken place.
When asked whether an ambulance was needed for the victim he said no, police should “just go in”.
His mother was dead, he confirmed.
The defendant was asked how serious the assault had been.
“Very,” he replied.
What type of assault had he committed?
“A murder,” he said.
When officers entered the home, they found the fire alarm sounding, a haze of smoke in the kitchen and the victim dead in her bed.
The murder weapon was on the floor of the hallway.
Half an hour later, the defendant was picked up at Fea St where he had been waiting in his blood-stained clothing.
The teenager, who appeared in court wearing a bright orange, prison-issue tracksuit, was remanded in custody and will be sentenced in August.
