A Northern Territory police officer charged with the murder of Kumanjayi Walker was justified in firing the first shot but the second and third were "excessive, unreasonable and unnecessary", a court has heard.
In a committal hearing for Constable Zachary Rolfe, US criminologist Geoffrey Alpert told the Alice Springs Local Court that after the first shot, Const Rolfe had time to reassess and use less lethal options to subdue Mr Walker.
"He had time, and the ability to go hands-on or use less lethal force, such as a Taser, were far more reasonable responses than going and shooting at very close range - two shots in the chest," Dr Alpert said.
In his report read in part to the court, the University of South Carolina professor said the second and third shots were not "reasonable, necessary, proportionate and appropriate to the circumstances".
"The second round of shots in close range to Mr Walker was excessive, unreasonable, and unnecessary," he said.
Dr Alpert told the court that he believed the first shot was reasonable because at that time Rolfe, Mr Walker and another officer were basically fighting and Rolfe had been stabbed with a pair of scissors.
"Once that event ended, and Constable Rolfe was able to disengage, my opinion is that he should have," Dr Alpert said.
"He had the time, the distance, and the opportunity to reassess the threat.
"He had the time and he had the ability and he had the space to reassess, and in my opinion reassessed improperly."
But he agreed with defence arguments that he could not know Rolfe's state of mind at the time in what was a tense, uncertain and rapidly evolving situation.
Mr Walker died after being shot as police tried to arrest him at a home in Yuendumu, 300 kilometres northwest of Alice Springs in November last year.
An immediate response team has been called in from Alice Springs to make the arrest after the 19-year-old had rushed at other officers with an axe three days earlier.
Rolfe has not yet entered a plea to the murder charge but previously indicated he would contest the allegations.
The committal hearing will determine if the matter proceeds to the Supreme Court for trial.
Rolfe is not attending the hearing in person but by video link from Canberra.
In earlier evidence, the court was played video from cameras worn by the three officers involved in the arrest which showed the struggle inside the house.
The hearing has also heard about police training which dictated that officers draw their guns if an offender produced an edged weapon such as a knife or scissors.
