The defence at a high-profile Dunedin murder trial has questioned the Crown's key witness.

Dr Venod Skantha is charged with murdering 16-year-old Amber-Rose Rush, who was stabbed in her bed at her Corstorphine home on February 2 last year.

A teenage associate of Skantha's has returned to the stand at the High Court at Dunedin today.

The teen has given a detailed account of how he says he was roped into driving Skantha to Amber-Rose's house the night she was killed - and later helped destroy the evidence.

But defence lawyer Jonathan Eaton says he seems to know far too much.

"You have way too much detailed information – unless you personally were involved in going into Amber's room and attacking her.

"We believe you were protecting your own position in order to implicate Dr Skantha."

Venod Skantha is charged with murdering 16-year-old Amber-Rose Rush. Photo / Christine O'Connor

He told the teen he must have been pretty chuffed he was able to solve the case for police.

"It was pretty quick-witted to think to leave blood on Skantha's shoe – and have him throw the phone somewhere where you could lead police to it.

"Don't you think it sounds like a pretty good script for a film? For a 16-year-old boy to set these traps for the 30-year-old doctor?"

The court is now hearing transcripts of some of the young witness's Facebook conversations.

Eaton has questioned why the teen tried to get in touch with media outlets.

It's been revealed the teen sent a Facebook message to Radio New Zealand (RNZ) two days after Amber-Rose's body was discovered.

It said: "I know stuff about the doctor charged with murder."

When asked why by the defence, he replied he liked attention.

The messages showed RNZ wanted an exclusive - and were prepared to send a camera crew to his house.

They set up a time to meet, but the teen says he was warned by police it wasn't a good idea.

He asked the RNZ reporter if he'd get paid for his story, to which they replied he would not.

Other Facebook messages to his friends show inconsistencies with his earlier testimony.

He told one friend that after killing Amber-Rose, Skantha threatened him with the bloody knife.

The teen says it was just an exaggeration.

He also sent a long message to Amber-Rose's mother - Lisa Ann Mills.

He apologised to her about a picture he'd put up, and told her he wanted to say he was sorry.

"When that scum [Skantha] got me to drive to your house, I had no idea what was about to happen. He pointed a knife at me and told me he'd kill me and my family."

The teen's admitted he was exaggerating - and says he doesn't know why.

He told another friend Skantha visited his house and tried to bash in the door, screaming he wanted to kill him and his mother.

"That would've been an exaggeration."

Eaton's also questioning him about his relationship with Skantha, and how he got so close with the doctor.

"I've always liked older things – music, movies, TV... I've always gravitated to older people."

He agreed with Eaton he saw himself as Skantha's right-hand man - and was quite proud to have a friend who was a rich, older doctor.

Eaton is also questioning the witness about his relationship with the young victim.

He presented messages to the court from several months after the witness first met Amber-Rose - where he'd professed his love for her.

She replied she didn't feel the same way.

He admitted they'd grown distant - after Amber-Rose woke to find him standing at the end of her bed one night.

The teen explained he was feeling depressed that night and just wanted to talk.

Eaton has put it to the witness that he was obsessed with her - which he strongly denies.