A Dunedin doctor allegedly offered a 16-year-old girl up to $20,000 for sex before later stabbing her to death, a court has been told.

Venod Skantha ,32, has pleaded not guilty to the murder of 16-year-old Amber-Rose Rush, who was found dead in her Corstorphine home in Dunedin on February 2 last year.

He also denies four counts of threatening to kill.

Amber-Rose was found by her mother Lisa Ann Rush dead in her bed, after sustaining six knife wounds to her neck and throat.

The victim was one of a large group of teens who the junior doctor was regularly associating with from 2017.

Crown prosecutor Richard Smith said Skantha was providing drugs and alcohol to the teens at social gatherings.

His friendship with Amber-Rose, the court heard, soured in early 2018 when he allegedly indecently assaulted her.

The victim's mother Lisa Ann Rush, who died of a suspected suicide last year, gave a police statement after her daughter's death.

"As a mother, I thought it was weird a 30-year-old was hanging out with 16-year-olds," she said.

Ms Rush recalled a time she picked Amber-Rose up from Skantha's home when she was unusually quiet and withdrawn.

One of the girl's friends later explained that the defendant had offered Amber-Rose money for sex. It began at $50 and ended at $20,000, they said.

"When I found out . . . I told her I wanted to kill him," Ms Rush said.

Amber-Rose ceased regular contact with Skantha until February 2018, when he accused her of using his credit card for online purchases.

She denied that, called him a "f***ing perv" and said he should own up to what he did.

The victim then posted screenshots from their conversation on Instagram, which sparked another online exchange in which the defendant asked the girl if she was serious about informing the authorities.

She said she was and told him: "You don't deserve to walk free."

Minutes later, Skantha allegedly asked a 16-year-old mutual friend to drive him to Amber-Rose's home and instructed he park round the corner from the house.

He said he had a "master plan" but would not reveal it, the boy said.

Skantha allegedly used a spare key to enter the home and muffled the girl's cries with a pillow before stabbing her to death.

One injury penetrated through to the bone and almost severed her ear, the court heard.

Smith said police found blood, likely to be Amber-Rose's, in the passenger side of Skantha's silver BMW.

Further blood was found on the inside of a plastic bag in which the defendant allegedly put his clothes before burning them at his girlfriend's home in Balclutha.

A pair of shoes at that address also had blood on them, the court heard.

Before dropping his teenage friend off at his home, Skantha allegedly threatened to kill him and three family members if he spoke of what happened.

Shortly after, however, the boy told his family and went to police.

Skantha also gave a statement in which he denied any role in Amber-Rose's death and downplayed the importance of the messages they had shared immediately prior.

"It was only the defendant who had a motive. That motive was significant," Smith said.

Just minutes before Rush stabbed to death in her bed, she had threatened to expose a Dunedin doctor as a sex attacker, a court earlier heard.

Smith told the court this afternoon that the allegations would likely have ended the defendant's medical career and could have seen serious charges laid by police.

"Obviously he had a great deal to lose," he said.

The court heard Skantha was on a final warning over his conduct at Dunedin Hospital and had only evaded the sack by telling bosses that his mother had died.

That was a lie, Smith said.

Defence counsel Jonathan Eaton QC, in his opening address this afternoon, told the jury the evidence the Crown relied upon to prove the charge was either untruthful or unreliable.

It was accepted, Eaton said, that Amber-Rose was killed in her bed by an intruder, "an intruder who knew how to get into the house in the dark of night, an intruder who knew where her bedroom was. That intruder was not Venod Skantha".

He told the court the idea that the defendant committed murder to protect his career did not fit.

"It makes no sense."

The trial before Justice Gerald Nation and a jury of 10 men and two women is set down for six weeks and will hear evidence from nearly 100 witnesses.