Constable Zachary Rolfe, 30, has pleaded not guilty to the 19-year-old's shooting murder in Yuendumu, 290km northwest of Alice Springs, on November 9, 2019.
After a lengthy delay behind closed doors on Tuesday, Justice John Burns told the Supreme Court in Darwin that one of the jury members had been discharged.
He held a ballot in open court to elect one of two reserve jurors to the main body of 12 to replace the juror.
"Both the accused and Crown have accepted the assurances given by the remaining members of the jury that they can address the issues raised in the trial in unbiased fashion," he said.
Justice Burns did not say why the jury member was discharged.
Mr Walker was shot three times after he stabbed Rolfe in the shoulder with scissors during a scuffle in an unlit bedroom.
The Crown has conceded Rolfe's first shot, which was fired while Mr Walker was standing and resisting arrest was justified.
But it says the fatal second and third shots went "too far".
Rolfe was sent to the outback community to arrest Mr Walker after he aggressively threatened two other officers with an axe.
The constable arrived about 7pm with three other heavily armed officers and was ordered by the local officer-in-charge, Sergeant Julie Frost, to find out where Mr Walker was.
She had also prepared a detailed plan to arrest Mr Walker about 5.30am the next day when the teen was likely to be sleeping and easily apprehended.
Rolfe and his team left the police station at 7.06pm and quickly located the troubled teen at a house about 15 minutes later.
He fired his first shot about 7.21pm as Mr Walker was standing and wrestling with him and another officer, Constable Adam Erbyl.
It was quickly followed by two more shots while Const Erbyl scuffled with the teen on the floor.
Mr Walker died at 8.36pm from injuries sustained by one of those two shots, which the Crown says were not legally justified because Mr Walker was "effectively restrained".
The trial's most explosive evidence has been Rolfe and Constable Eberl's body-worn camera footage of the shooting.
The confronting video shows the moment Rolfe fires three rapid shots in 3.1 seconds into Mr Walker's body.
Mr Walker can be seen holding the scissors in his right hand after Rolfe fires his first shot into the teen's back.
The dark and grainy video then shows Rolfe firing his Glock pistol into Mr Walker's left torso from "point-blank" range.
Played at normal speed the incident is chaotic, occurring almost instantaneously as the three men shout and struggle.
The trial continues.
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