A murder-accused policeman's fatal second shot into an Aboriginal teenager was not reasonable, an expert witness has told a Darwin jury.
Constable Zachary Rolfe, 30, has pleaded not guilty to murdering Kumanjayi Walker, 19, after the teen stabbed him in the shoulder with a pair of scissors on November 9, 2019.
Rolfe fired three shots into Mr Walker as he resisted arrest in a room at his grandmother's home in Yuendumu, 290km northwest of Alice Springs.
The teen died after the second shot ripped through his spleen, lung, liver and a kidney.
Expert witness Detective Senior Sergeant Andrew Barram reviewed Rolfe's body-worn camera video and says the constable's second and third shots were not reasonable.
Rolfe fired them after Mr Walker had fallen to the ground with another officer, Sergeant Adam Eberl, who was then a constable, on top of him.
"Things had changed substantially since the first shot was fired," Det Sen Sgt Barram told the Northern Territory Supreme Court on Tuesday.
"They had gone from standing in an equal fight to being on ground with Constable Eberl on top."
The former officer-in-charge of the NT Police operational safety section also said Rolfe's first shot was justified "because he was confronted at close range with an edged weapon and stabbed with it".
"It is reasonable to believe his partner was also in danger."
Det Sen Sgt Barram said Rolfe should have shouted "knife, knife, knife" if he was aware Mr Walker was armed.
"It is part of communicating to let his partner know just in case they have not seen it," he said.
Earlier, he said Rolfe and Sgt Eberl should have ordered Mr Waker to show his hands when the teen first came into view across a dark room.
"They should not have gone (into the house) if they suspected it was Mr Walker," he said.
"He is clearly a high-risk offender with a propensity to previously arm himself."
He said Rolfe and Sgt Eberl should not have allowed the teen to get so close.
"The first thing that is immediately apparent when Mr Walker comes into view is that he has got his hand in his pocket," Det Sen Sgt Barram said.
"They have put themselves in close proximity to someone that they suspect was armed."
Rolfe and three other officers were sent to the remote Indigenous community to assist local officers with general policing duties.
They were also ordered to arrest Mr Walker at 5.30am on November 10 when he was likely to be sleeping and easily taken into custody.
Instead, they found the teen about 15 minutes after leaving the local police station where the officer-in-charge Sergeant Julie Frost has said she handed the men a printed page outlining the arrest plan.
Rolfe walked into a dark room and shot Mr Walker about a minute later. The second fatal shot ripped through the teen's spleen, lung, liver and a kidney.
The Crown says Rolfe and his team were "intent" on finding Mr Walker after watching a video of him violently threatening two other policemen with an axe on November 6.
It has conceded the first shot, which was 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".
The trial continues.
