Rolfe has pleaded not guilty to murdering the 19-year-old during a failed arrest attempt in Yuendumu, 290km northwest of Alice Springs, on November 9, 2019.
He shot Mr Walker three times and says he was doing his job and defending himself from a violent offender who had stabbed him in the shoulder with a pair of scissors.
Sergeant Adam Eberl told the Northern Territory Supreme Court on Tuesday he did not think Mr Walker was a threat to him or Rolfe as the teen walked towards them.
Sgt Eberl and Rolfe had earlier watched body-worn camera footage of Mr Walker violently threatening two other officers in Yuendumu with an axe three days earlier.
The incident had contributed to the decision to send Sgt Eberl, then a constable, and Rolfe to the community but he said he did not notice if Mr Walker had his hands in his pockets as he approached the men.
"When I was there no, not until watching the body-worn after," he said.
Sgt Eberl also said he did not think to ask Mr Walker to show his hands to the officers as he moved closer or believe he would need to "gain control" of the teen.
Body-worn camera footage shows Mr Walker telling the officers his name is Bernard Dixon before one of them orders him to put his hands behind his back in order to arrest him.
He does not do it and seconds later the men begin scuffling. Mr Walker then stabs Rolfe in the shoulder with scissors held in his right hand before three shots are fired.
The second fatal shot left a "gaping hole" in the teen's right lung after ripping through his spleen, liver and left kidney.
He died because "he was not able to breathe" and from blood loss.
Prosecutors have conceded the first shot, which was fired while Mr Walker was standing and resisting arrest, was justified.
But they say the second and third shots went "too far" because the teen was "effectively restrained" on the ground by another officer when Rolfe pulled the trigger.
Sgt Eberl also said he was not given an order before the shooting to arrest Mr Walker at 5.30am the following morning when he was likely to be sleeping and more easily taken into custody.
Earlier on Tuesday, forensic pathologist Marianne Tiemensma told the court the teen would not have been able to significantly injure either officer using the "small and blunt" scissors he was armed with.
"I do not think that pair of scissors would have caused fatal injury," she said when asked if they could lacerate an artery.
"Fatal stab injuries by scissors are not common.."
Dr Tiemensma said Mr Walker also had limited opportunity to attack the officers because Const Eberl moved to restrain him the moment "he pulled the scissors from his pocket".
"Within seconds he is partially restrained with Eberl moving in behind him, grabbing him around his right shoulder and the neck ... so there is decreased movement of his right upper limb."
She said he would not have been "able to generate enough force" to break through the officers' clothing "into the skin and soft tissue and structures of importance to cause serious injury".
Dr Tiemensma also found that Rolfe's first shot into the right side of the teen's back would not have killed him, as it lodged in muscle and did not result in excessive bleeding.
She said Mr Walker had a very low blood alcohol level the night he died and an insignificant amount of cannabis in his system.
The trial continues Wednesday.
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