On a Dunedin doctor's shoe was a droplet of blood which likely came from the teenager he allegedly stabbed to death, a forensic scientist says.

She also found what could have been 16-year-old Amber-Rose Rush's blood on the passenger side of the defendant's silver BMW and the inside of a plastic bag in which he allegedly stashed his stained clothes, the High Court at Dunedin heard this morning.

Venod Skantha, 32, is on trial accused of murder and four counts of threatening to kill.

The Crown says he inflicted the six stab wounds to the victim's neck as she lay in the bedroom of her Corstorphine home late on February 2 last year, to protect his medical career.

Amber-Rose had told him she was planning to make sexual allegations to both police and the defendant's Dunedin Hospital superiors, just minutes before she was killed.

ESR's Rosalyn Rough told the jury of her findings in relation to the victim's home at Clermiston Ave, Skantha's in Fairfield and his ex-girlfriend's in Balclutha.

Among her key findings, she said, were spatter stains on the inside of passenger window of the defendant's car.

They could have been flicked or cast off a blood-stained object, Rough told the court.

It was probably Amber-Rose's blood, she said.

Tests also revealed there was a transfer stain on the inside of the passenger door, which would likely come from a bloody surface coming into contact with it.

The DNA profile could have been a combination of the defendant and Amber-Rose, the jury heard.

Amber-Rose Rush was killed in her Dunedin home in February 2018. Photo / Facebook

The Crown's key witness – the teenager who allegedly drove Skantha to and from the scene of the crime – said the defendant was in the passenger side of the car as they left the address.

He told the court earlier this week he had seen the doctor place the bloodied knife inside the side pocket of his door.

Rough tested that area and found no evidence of blood.

She also confirmed there was no blood found on the driver's side of the car or inside the boot.

The 24cm stainless-steel kitchen knife the Crown says was the murder weapon was analysed by scientists, along with the other blades and a knife block found in Skantha's home.

No blood was detected, the witness said.

After the alleged murder, Skantha and his teenage friend travelled to Brigid Clinton's house in Balclutha where they spent the next two nights.

The teenager previously told police the defendant had taken his clothes there in a bag where they were burned in a plant pot.

Rough said there were blood "flecks" inside a white supermarket bag found at the property which could have been from Amber-Rose.

The teenager also gave evidence he had been instructed to wash Skantha's grey suede shoes but had deliberately left a clear area of blood for police.

Rough found diluted areas of blood consistent with washing but there was an untouched droplet on the top of one of them likely from Amber-Rose.

Such an elliptical spot, she said, could have come from blood falling directly onto a surface or dropping onto it from another blood-stained object.

The scientist confirmed there was nothing at the Clermiston Ave scene that linked clearly to Skantha.

She said there was no evidence of a struggle in the bedroom – usually in the form of spatter stains – and the victim likely bled to death on her front where she was attacked.

The trial continues.