Rolfe, 30, has pleaded not guilty to murdering the Aboriginal teenager during a failed arrest attempt in Yuendumu, 290km northwest of Alice Springs, on November 9, 2019.
He says he was doing his job when he shot the 19-year-old three times and defending himself and Remote Sergeant Adam Eberl from a violent offender who had stabbed him in the shoulder with a pair of scissors.
Body-worn camera footage of the incident played in the Northern Territory Supreme Court on Wednesday shows Sgt Eberl, then a constable, hit and then forcefully grab Mr Walker seconds before Rolfe fires his first shot.
Sgt Eberl told the court he spotted a "sharp and pointy object" in the teen's right hand.
Asked why he did not also drawn his Glock pistol as Rolfe had, Sgt Eberl said he was not aware Mr Walker had a weapon when he started restraining him.
"When you did become aware why did you not draw it?" prosecutor Philip Strickland SC said.
"Because his right arm was out and it was not in front of me trying to stab me at that time," Sgt Eberl replied.
"I took hold of his arm, and I used a distraction strike to try and change his mindset, and get him into a position to grab him and try and restrain him."
Sgt Eberl is then seen holding Mr Walker from behind with his right arm around his neck and his left arm locked around the teen's left arm before the pair fall to the ground.
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 Sgt Eberl when Rolfe pulled the trigger.
Sgt Eberl described the sound of the first shot as a "dull thud" and said he thought it was another officer, Constable James Kirstenfeldt, firing a non-lethal beanbag round from a shotgun.
It was followed 2.6 seconds later by the second and third shots when Sgt Eberl has Mr Walker on the ground on his side.
Sgt Eberl can then be heard on the video telling Mr Walker "stop f***ing around or I will smash you" after the Rolfe fires the shots from behind him.
Rolfe then says "it is all good, he has got scissors, he was stabbing me, he was stabbing you" as he and Sgt Eberl struggle to handcuff the moaning teen.
"I was trying to restrain him on the ground. I was holding his left arm with my arms. To prevent him trying to get me with the weapon he had in his hand," Sgt Eberl told the court.
Asked where Mr Walker's right arm and hand holding the scissors were at that time, Sgt Eberl said "I believe it was sort of underneath his body".
He previously told the court he did not think Mr Walker was a threat to him or Rolfe as the teen walked towards them.
The officers 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 and Rolfe to the community.
The officers' body-worn camera footage also shows Mr Walker telling the Rolfe and Sgt Eberl his name is Bernard Dixon and one of them ordering him to put his hands behind his back.
The teen resists arrest and the men start wrestling. One of the officers yells "stop it mate". Mr Walker then stabs Rolfe in the left shoulder with scissors held in his right hand before three shots are fired.
The trial continues on Thursday.
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