So his actions on April 4 left many wondering "what did I miss?" the woman said.
Borton was at his flat on Lemnos Ave in the high-end suburb of Karori that evening when he saw the victims go into a nearby property to use the laundry.
Taking a steel mallet that he'd earlier stolen, Borton went into the house and surprised the girl, who was looking for a house cat.
She immediately recognised him and said hello, but as she turned to catch the cat, Borton swung the mallet at the back of her head, sending her flying.
"The defendant placed one hand around her throat and his other hand over her nose and mouth. She struggled for breath," the summary of facts said.
The girl clawed at his hands, screamed, and tried to bite Borton's fingers, but was unable to get away from him.
He then struck her again in the head, this time caving her skull inwards and knocking her unconscious.
The 52-year-old victim heard the girl scream and came to help her, but as she entered the room Borton struck her repeatedly in the head with the mallet, fracturing her skull and causing heavy blood loss.
As she lay dying on the floor, he undressed the girl and sexually violated her, telling her "it's okay".
The girl then watched as he went over to the dying woman, who was groaning in pain. She fell unconscious again and Borton began undressing the woman.
Borton then returned to his own flat and showered, before coming back to clean up the blood from the victims' head injuries, the summary said.
When the girl regained consciousness again, Borton came into the room and told her there had been an earthquake, injuring her and her mother. He said her mother had gone to hospital and would be back soon.
He then undressed himself and lay down by the girl, saying "let's play". The girl lost consciousness again.
The next day Borton called 111 and said he had killed the woman, referring to himself as a "peeping Tom".
An autopsy revealed the woman suffered at least eight separate head injuries so significant that fragments of her skull were pressed into her brain.
The 12-year-old needed surgery to reconstruct her skull.
A scene examination uncovered the bloodied mallet in a bathroom sink with various other items, including a used condom.
Borton told police he intended to "incapacitate" the 52-year-old so he could sexually offend against the daughter.
He described the sexual offending in detail.
Police found the woman's body about 1.10pm on April 5, and the seriously injured girl in the same room.
Both victims have name suppression.
Borton's offending also includes stealing photographic equipment worth more than $4600, and clothing. A phone seized by police contains photos of an apparently oblivious woman wearing the clothing that Borton later stole.
He has been convicted and given a strike warning, and will be sentenced in October.
