Australia's highest court has thwarted a police officer's bid to argue he acted in "good faith" in the alleged murder of an Indigenous man.
Prosecutors successfully challenged the key tenet of Constable Zachary Rolfe's defence in his pending trial for the alleged murder of 19-year-old Kumanjayi Walker.
He was shot three times after stabbing Rolfe with a pair of surgical scissors while being arrested in the remote Northern Territory community of Yuendumu in November 2019.
The full bench of the High Court on Wednesday ruled in favour of prosecutors seeking to stop Rolfe relying on an immunity clause contained in the territory's Police Administration Act.
It provides a protection from civil and criminal liability for actions performed in "good faith" during the exercise of police power.
"The common law and statutory powers are subject to constraints, such as doing only that which is reasonable and necessary," the High Court said.
It deemed an earlier Northern Territory Supreme Court decision clearing the way for Rolfe to use the immunity clause before the jury "overbroad and erroneous".
"It has been necessary for this court to correct that error but it should not be assumed that this court will do so in every case."
Prosecutor Philip Strickland SC earlier argued the decision would have significant repercussions for the use of police powers, with cases in South Australia on hold pending the ruling.
Mr Strickland said the national significance of Rolfe's case was heightened because it involved an Indigenous man.
He feared a liberal construction of immunity clause could leave citizens vulnerable to police abuse or excess and lead to Rolfe's acquittal on an incorrect basis.
Rolfe is charged with murder, and the alternative offences of manslaughter and engaging in a violent act causing death.
Acting for Rolfe, Bret Walker SC maintained the possibility of an acquittal was not a sufficient reason to allow the appeal.
He did not want Rolfe's case to be fragmented and stressed the immunity clause provided protection for officers tasked with making split-second decisions.
The High Court acknowledged the barrister's concerns.
It said it had "emphasised on many occasions how rare it is to make orders which would have the effect of fragmenting the ordinary course of criminal proceedings".
"The reasons why it is highly undesirable to do so are obvious. They include delay and its effects. That is why the hearing of this application was expedited," the court said.
Rolfe's trial has been pushed back multiple times including pending the determination of the immunity clause.
The case is due to return to the territory's Supreme Court next week and a trial is scheduled for February.