A teenager, allegedly stabbed to death by a Dunedin doctor, would have taken "some minutes" to die from her wounds, a pathologist says.

Venod Skantha, 32, has pleaded not guilty to the murder of Amber-Rose Rush and four other charges of threatening to kill at the outset of his trial before the High Court at Dunedin this week.

The Crown told the jury in the opening address that the doctor had been messaging the 16-year-old victim only minutes before her death at her home in Dunedin, late on February 2 last year.

Amber-Rose told him she was planning to tell police and Dunedin Hospital bosses that Skantha had sexually assaulted her and others, and that he was supplying alcohol to minors.

"I'm doing the world a favour," she wrote. "People like you don't deserve to walk freely."

The Crown says Skantha found out Amber-Rose had posted screenshots of their conversation on social media and he then recruited a teenage friend to drive him to the girl's Corstorphine home.
The defendant allegedly used a spare key to get inside, then stabbed her six times in the neck while she lay in her bed, taking her cell phone and leaving her to die.

Forensic pathologist Dr Kate White gave evidence at court today. She completed her autopsy on February 5, 2018 and found that Amber-Rose died "as a result of an incised wound to the left side of the neck".

The injury that caused her to bleed to death sliced through her earlobe and hit the base of her skull.

Dr White told the jury the 11cm-long wound hit her carotid artery and breached the windpipe too. Due to its length, it was not a "classic stab wound", she said.

Crown prosecutor Robin Bates cautioned the jurors before providing them with photo booklets depicting Amber-Rose's body.

He asked the pathologist how much force would likely have been required to cause such damage.

"It's a very difficult question to answer and there's no way of precisely answering that," Dr White said.

She told the court the damage to bone suggested at least moderate force, but that also depended on the sharpness of the knife used.

The severance of the carotid artery, which takes a large volume of blood to the brain, meant the victim would have ultimately "bled out" without medical attention.

How long would it have taken? Mr Bates asked.

"Some minutes," said Dr White.

As well as the fatal injury, she also identified stab wounds to the back of the neck and two "superficial" horizontal cuts to the girl's throat.

None of those would have contributed materially to her death, the pathologist said.

In cross-examination, Jonathan Eaton, QC, asked whether the witness could determine whether the killer was right or left-handed.

It was "notoriously unreliable" to speculate on that, Dr White said.

She explained she did not measure the depth of the wounds because it was not a reliable way of estimating the length of the blade used to create them.

She had not examined any weapon which allegedly caused the injuries.

Yesterday the jury heard how Skantha allegedly toasted marshmallows while burning the bloody clothes he wore to commit the murder.

Later, his ex-girlfriend said, they met Amber-Rose's grieving mother Lisa Ann Mills and bought her flowers and a card before suggesting who may have been responsible for her death.

The trial continues.