Even if a jury believes a Dunedin doctor was assisted in his alleged stabbing of a teenage girl he can still be found guilty of murder, a judge says.

Venod Skantha, 32, is on trial in the High Court at Dunedin accused of killing 16-year-old Amber-Rose Rush as she lay on her bed at her Corstorphine home on February 2 last year.

He is also charged with threatening to kill a teenager, the prosecution's key witness who drove him to and from the scene, and three of that boy's family members, in a bid to stop him telling police.

Justice Gerald Nation summed up the various elements of the trial this morning after the 10 men and two women of the jury heard closing addresses from both Crown and defence yesterday.

As he did at the trial's outset more than three weeks ago, the judge stressed jurors should continue to disregard anything they had previously heard about the case or any reports they had read, particularly "sensationalist" headlines.

Justice Gerald Nation in the High Court at Dunedin.

He warned them they may have sympathy for those affected by the alleged murder but it must be put to one side when they considered the evidence.

Similarly, Justice Nation said any prejudice was inappropriate.

"You may not have liked or approved of the way a 30-year-old doctor associated with people much younger than himself, or the way they made use of him – his home, his car, his money," he said.

The Crown said Skantha's motive to kill Amber-Rose was clear.

She had threatened to make disclosures about him "touching up" girls, offering them money for sex and plying minors with alcohol.

The fragility of his medical career at Dunedin Hospital, where he was on a final warning, drove him to murder, Crown prosecutor Robin Bates said.

Defence counsel Jonathan Eaton QC said such an extreme reaction made no sense.

He was highly critical of the Crown's star witness, the teen who told the court Skantha had gone into Amber-Rose's home and come out with a bloodied knife, her phone and driver's licence.

He told the jury in closing that if they believed that witness had lied and actually been involved in the killing in some way, they must find his client not guilty.

Justice Nation today said that was wrong.

As long as the jury found Skantha killed Amber-Rose, they should find him guilty, he said, regardless of whether the teen may have lied about the prelude or aftermath.

The judge said if they decided a witness had told lies, it did not mean they should completely discard the rest of that person's evidence.

A question trail was presented to the jury to assist them in reaching verdicts.

However, Justice Nation said, ultimately the issue was clear.

"The person who stabbed Amber-Rose . . . must have intended to kill her," he said.

But was it Skantha who had wielded the knife?

The jury will retire to commence deliberation once the judge's summing up has concluded.

Crown, defence closing arguments

The Crown says a Dunedin doctor killed a teenage girl with "one quick incision" as she lay in bed, but the defence has rubbished the prosecution's theories.

Yesterday the jury heard both Crown and defence closing addresses before they begin their deliberations today with more 1000 pages of evidence and numerous exhibits at their fingertips.

Amber-Rose Rush was murdered in her bed.

Crown prosecutor Robin Bates said Skantha's motive was clear: Amber-Rose had threatened to tell police and his hospital superiors about him "touching up" girls, offering them money for sex and supplying alcohol to minors.

The prosecutor said not only was the doctor's job important to him but he was on a final warning for misconduct at the time.

"Amber alone could bring his career to an end; years of training, costs involved — down the drain, all over rover," he told the jury.

But defence counsel Jonathan Eaton QC said the suggestion a young doctor would kill a girl to protect his career was fanciful.

"If anything doesn't make sense in this case, it's that theory," he said.

Similarly, Eaton told the court, it was illogical he would go to the victim's Corstorphine home with a 16-year-old driver and subsequently confess to him.

The lawyer said the evidence that the defendant groped the victim as she suggested did not stack up in any event, which was why the girl went back to his house after the alleged incident.

Dr Venod Skantha on trial for the murder of Amber-Rose Rush.

Eaton accepted Skantha had offered Amber-Rose $20,000 for sex but said that had been fuelled by alcohol and was certainly not serious.

Bates told the jury it was significant Amber-Rose was dead within 30 minutes of her last message to Skantha on February 2 last year, and that her phone was taken.

The Crown prosecutor said whoever went inside the Clermiston Ave home in the middle of the night was taking "a massive risk".

"The person who took that risk had to have a very compelling and immediate reason to be there," he said.

Eaton said the police case against his client was "blinkered", and he was highly critical of the Crown's key witness — the teenage driver who was with his client from February 2-4.

He suggested the jury should have heard "screaming alarm bells" when the man called himself a "compulsive liar" in an interview with police.

"This is a story of violence, trauma, emotion, threats, fear. Throughout these interviews we don't see any emotional response from [him]," Eaton said.

It was a different story in court.

The lawyer said the witness did not stand up to scrutiny.

The teenager used the phrase "I can't remember" 161 times and asked for a question to be repeated 26 times, he noted.

While Bates acknowledged the witness was unusual, he said there was a generally clear version of events.

"He's not a person who would viciously kill a friend, a person who was good to him," he said.

Bates said the person who stabbed Amber-Rose, severing her carotid artery and trachea, knew what they were doing, consistent with Skantha's training as a doctor.

"[It was] a focused attack ... to shut Amber up with one quick incision," he said.

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

The defence had a different theory.

The key witness, Eaton told the jury, was infatuated with the young doctor.

"He was in awe of this guy, obsessed with his car ... loved being his driver," he said.

"He treasured that relationship. I suggest he'd do anything to protect Venod Skantha."

When Skantha was questioned by police two days after Amber-Rose's death he denied any involvement.

The Crown said the defendant lied throughout and tried to distance himself from the victim.

Eaton, though, stressed his client gave the statement voluntarily and without a lawyer and his demeanour only changed when the accusations began flying.

"He was hurt by it; offended, shocked and hurt," he said.

It might have crossed jurors' minds, Eaton said, that both Skantha and his teenage associate were involved in the stabbing.

But that was not the Crown case, and if they were unsure, they must acquit the defendant, he said.