Dr Venod Skantha, accused of killing Amber-Rose Rush, 16, appears for trial in the High Court at Dunedin.

The self-styled wingman of Dr Venod Skantha killed the teen who threatened to ruin his friend's medical career, a jury has heard.

Jonathan Eaton QC took aim at the Crown's case during his closing statement in the High Court in Dunedin on Tuesday afternoon. He told the jury just one person was responsible for murdering Amber-Rose Rush: Skantha's teenage friend who had become the Crown's star witness.

"He is the person who is at the heart of this case," Eaton said before a packed gallery.

SUPPLIED Amber-Rose Rush, 16, was found dead in her Dunedin home in February 2018.

Skantha – who was arrested two days after 16-year-old Amber-Rose was killed in her bedroom on February 2 last year – denies murdering her, as well as four charges of threatening to kill.

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﻿The Crown alleges Skantha, 32, needed to silence Amber-Rose after she posted a series of messages between the pair on Instagram, which would have ended his already faltering medical career.

John Kirk-Anderson/Stuff Venod Skantha is on trial for the murder of Dunedin teenager Amber-Rose Rush.

Skantha, who was on a final warning at Dunedin Hospital, had everything to lose, the Crown argued.

The Dunedin doctor was treated as a "sugar daddy" by some teens, including the victim and the key witness, supplying them booze and offering them a place to party, Eaton said.

"They are using him."

JOHN KIRK-ANDERSON/STUFF Defence counsel Jonathan Eaton QC says the police had "blinkers on" while investigating Amber-Rose's death.

The star witness was Skantha's self-styled "wingman" who often drove the doctor's late model BMW, including on the night Amber-Rose was killed.

"I suggest he would do anything to protect Venod Skantha," Eaton said.

The witness, whose name is suppressed, was an "unusual person", who claimed he set the trap to solve the case – a bloodstained shoe left in a Balclutha garage.

JOHN KIRK-ANDERSON/STUFF Prosecutor Robin Bates arrives at court on the opening day of the murder trial for Venod Skantha. The Crown is delivering their closing arguments on Tuesday.

"He is living in a different world to us, it is a fantasy world."

The witness told some friends about the Instagram post and was concerned the man he knew as Vinny could lose his job, Eaton said.

Skantha had been falsely implicated by the witness, and the jury must decide if he was credible and reliable.

JOHN KIRK-ANDERSON/STUFF The Dunedin house where Amber-Rose was murdered.

Eaton urged the jury of 10 men and two women to "acquit Dr Skantha" if they doubted the witness' evidence.

Eaton said Skantha was cooperative, calm and truthful when answering questions during a voluntary interview with police, until the questioning took a different turn.

Thirty minutes into the interview, Detective Wayne O'Connell began asking questions that pointed at Skantha being the prime suspect in Amber-Rose's death.

Eaton told the jury his client was in shock and asked if the accusations had come from the Crown's star witness.

Later in the witness box, the star witness developed a "default mechanism", saying "I don't remember" 161 times, "give me a minute" 18 times and "can you repeat the question" 26 times, Eaton said.

He never said those words during three interviews with police, but did admit he was a "compulsive liar", Eaton said.

Crown prosecutor Robin Bates earlier said Skantha killed Amber-Rose because she had threatened his job, lifestyle and liberty.

Eaton said that motive was "illogical", particularly as the police never questioned a possible motive for the witness.

He took aim at the police handling of the case, which included telling the teen he was a witness and not a suspect.

"From there, there is no going back."

Eaton said the prosecution had "blinkers on" when handling the witness.

The relevance of some of the Crown's propensity evidence, including several teens who raised alleged concerns about Skantha, was designed to blacken his character, Eaton said.

THE CROWN SUMS UP

Bates told the jury Skantha entered Amber-Rose's home with a spare key, before stabbing her with a knife he brought from his home.

Amber-Rose was stabbed twice in the back – a reference to a previous message about her being a "back stabber".

"The person who did this, was really, really angry."

Bates said Skantha knew to target Amber-Rose's carotid artery and windpipe, as it was "all part of his training" as a doctor.

The attack was not some "random clumsy attempt", but a focused attack designed to silence Amber-Rose.

Bates said the killer was "hellbent on getting rid of the contents of [Amber-Rose's] phone", and the evidence pointed to one person: Venod Skantha.

Bates earlier told the jury that the case, which included more than 1000 pages of evidence, was "difficult and confronting".

Skantha did not take the stand during the trial, and his defence counsel called no witnesses.