"No-one could survive that,'' Venod Skantha (32) reportedly said after allegedly stabbing 16-year-old Amber-Rose Rush to death in the bedroom of her Corstorphine home.
He is on trial before the High Court at Dunedin where yesterday the Crown's key witness - a teenage boy who drove Skantha to and from the scene - told the jury about the night of February 2 last year.
He recalled seeing Amber-Rose posting a screenshot on Instagram that evening showing a heated exchange with the defendant, in which she accused him of molesting young people.
The Crown said once Skantha had been shown the post by his teenage friend, his murderous intent took root.
The teenage boy - who cannot be named because of his age - told police over the course of three interviews how the doctor picked him up and had him drive to the victim's home.
Skantha was wearing dark clothes, a hat and gloves, the witness said.
He looked "focused, you know, but chill''.
Skantha allegedly told his friend he had "a master plan''.
"Literally, I just thought he was going to go in and yell at her,'' the teenager said.
"I felt a little bit weird but I thought Vinny's not the type to abuse women.''
After being told to park round the corner from the Rush house, he told the jury he called a friend to chat.
"I do over-exaggerate a lot,'' the boy said.
He called the murder a ``one-man job'' and stressed he could never have known what was going on inside the house.
"I didn't think my best friend was going to murder my other friend in cold blood,'' the witness said.
However, when Skantha returned a few minutes later, he said he realised there was a problem when the man asked him to open his door and attach his seatbelt for him.
"I looked down and I could see him holding Amber's phone ... I could see Amber's face on the [driver's] licence; it was covered in blood,'' the boy said.
"I saw the knife, clear as day.''
The witness said he had been with Skantha when he bought the kitchen utensil as part of a set a few weeks earlier.
"That thing will be sharp,'' the teenager had said.
The pair allegedly drove out to Blackhead Quarry where they disposed of Amber-Rose's phone before heading to Skantha's Fairfield home, where the clean-up began.
The boy told the police he deliberately left a blood spot on the doctor's grey suede shoe and indicated where officers would find it.
Likewise, he said he did a sloppy job of cleaning other areas, so there would be a trail of evidence police could follow.
As Skantha put his bloody clothes into a bag, he allegedly confessed to the murder.
"I killed her,'' he allegedly told the teen.
After that, the duo drove to the defendant's ex-girlfriend's house in Balclutha, where they had a fire the next day.
It is alleged Skantha burned his clothes as well as Amber-Rose's driver's licence in a large plant pot he bought from The Warehouse.
"Amber's licence going up in flames - I've still got that image in my head,'' the witness said.
He told police he spent the two days after the murder pretending not to be upset.
"I just had to act like the old me,'' the boy said.
"I was just very afraid. I couldn't say anything, really.''
He told the jury he was also concerned for Skantha's ex-partner, Brigid Clinton.
"If he's done it once he can do it again,'' he said.
He conceded to police that, although he was a "compulsive liar'', he said he had told the truth about what happened that night.
When he was left alone in the interview room he spoke to the camera: "Whoever sees this recording ... I wish I could've done something that night that would've changed it and made a difference. I'm deeply sorry for what's happened here.''
