Detective Senior Sergeant Andrew Barram, the final witness for the prosecution in the Zachary Rolfe murder trial, continued to give evidence on Tuesday.

He formerly led the Operational Safety Section of the Northern Territory Police training college, which provides specialist skills training in firearms, defensive tactics and incident management.

During questioning from Crown prosecutor Philip Strickland SC, Senior Sergeant Barram was critical of the way Constable Rolfe and his partner at the time, Remote Sergeant Adam Eberl, conducted themselves as they attempted to arrest Mr Walker in his grandmother's house in Yuendumu on the evening of November 9, 2019.

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He said they should have established a cordon around the house they believed Mr Walker was inside. This would have been possible with the number of officers deployed from Alice Springs to Yuendumu that night.

Constable Rolfe and Sergeant Eberl instead entered the house and approached Mr Walker. Constable Rolfe held a photo on his phone next to Mr Walker's face in order to identify him.

Mr Walker pulled out a pair of scissors and stabbed Constable Rolfe in the shoulder, prompting Constable Rolfe to fire the first shot - a shot Senior Sergeant Barram said was justified.

"Because he was confronted at close range with an edged weapon, was actually stabbed with it in his shoulder, and it would have been reasonable to believe that his partner was also, at that point, in danger," Senior Sergeant Barram told the court.

Sergeant Eberl grabbed Mr Walker from behind, pulled him onto the floor and was on top of him when the second and third shots were fired, 2.6 and 3.1 seconds after the first.

The teen died after the second shot ripped through his spleen, lung, liver and a kidney.

When asked if he believed these shots were "reasonable or necessary", Senior Sergeant Barram said they were not.

"Things had changed substantially from when the first shot was fired," he said.

"They've changed from being in a standing position, in a fairly equal fight, to Mr Walker being shot in the back, which would affect a person in some way, and being pinned on the ground with his right arm under him."

He said there were other, non-lethal options available to Constable Rolfe at that time.

"He could have used his defensive tactics to help Mr Eberl control Mr Walker ... moving in and ... helping take control of Mr Walker on the ground," Senior Sergeant Barram said.

"As far as the fight was concerned, or the arrest of Mr Walker, the firing of those two shots made no difference to the tactical situation."

In cross-examination, Constable Rolfe's lawyer, David Edwardson QC, showed the jury a video of a police shooting in the US that Senior Sergeant Barram had shared on Facebook around one month before Mr Walker's death.

Senior Sergeant Barram had added the caption "Brings a little bit of reality into the argument," the court heard.

"It's plain is it not, that we can see the police officers - the first police officer who shoots the offender, constantly trying to distance himself from the offender?" Mr Edwardson asked, referring to the video.

Senior Sergeant Barram replied, "Yes".

Mr Edwardson asked, "The offender's armed with a knife?"

Senior Sergeant Barram replied, "Yes."

Mr Edwardson asked, "And then as he gets closer and closer, and we get to that critical distance, he then discharges his firearm ... multiple times?

Senior Sergeant Barram replied, "Yes."

Senior Sergeant Barram also agreed with Mr Edwardson that his perception of Constable Rolfe's body worn camera footage of the shooting "might be quite different from the person who is under attack".

Mr Edwardson is expected to continue his cross-examination of Senior Sergeant Barram on Wednesday.

The trial continues.