An Aboriginal teenager remained a threat after police shot him three times, an expert witness has told Constable Zachary Rolfe’s murder trial.

Rolfe, 30, has pleaded not guilty to murdering Kumanjayi Walker, 19, during a failed outback arrest on November 9, 2019.

He fired three shots into Mr Walker’s back and torso after the teen stabbed him with a pair of scissors in Yuendumu, 290km northwest of Alice Springs.

Law enforcement expert Ben McDevitt told the Northern Territory Supreme Court on Tuesday that Mr Walker remained dangerous after he was shot.

“The struggle had gone to the ground but it was still an extremely active struggle,” he said in response to questions from Rolfe’s lawyer David Edwardson QC.

“Throughout that struggle Mr Walker remained armed with the edged weapon and it would appear, certainly by his statement after the third shot, that he intended on using it.”

Rolfe’s body-worn camera footage of the incident shows Mr Walker saying “I am going to kill you mob” as Rolfe and his partner Sergeant Adam Eberl, then a constable, handcuffed him after he had been shot three times.

Mr McDevitt also said the anger faced by Sgt Eberl increased after Rolfe fired his first shot into Mr Walker’s back because he and the teen fell to the ground.

“It is far more difficult in a ground struggle to be able to retain your own weapon, so not only was there the threat of the edged weapon but it’s easier, in my view, to be able to take a weapon from somebody.

“There is a lot of latent power in that ground struggle, things can change incredibly quickly.”

Mr McDevitt also said Sgt Eberl would no longer have been able to use his legs to run from or defend himself against Mr Walker.

He said his overall assessment was that Rolfe’s actions, given the information the constable had at the time, had been in accordance with his police training.

But he conceded while questioned by prosecutor Philip Strickland SC that Rolfe and Sgt Eberl appeared to have gone into Mr Walker’s home without a plan and they failed to adequately communicate with other officers positioned around the house when they found the teen.

The Crown has conceded the first shot, fired while Mr Walker was standing and wrestling with Sgt Eberl, was justified.

But it says the second and third shots, which are the subject of the murder charge, went “too far”.

Mr Walker died about an hour after the second shot ripped through his spleen, lung, liver and a kidney.

Defence lawyer David Edwardson QC called Rolfe as a witness last week.

The constable told the court that before he pulled the trigger the teen grabbed at his police-issued pistol.

He also said he saw the teen repeatedly stab Sgt Eberl and that he feared for his and his partner’s lives during the incident.

The trial continues.