Murder-accused NT cop's Taser battery flat

Rolfe fired three shots into Mr Walker's back and torso as he resisted arrest at his grandmother's home in Yuendumu, 290km northwest of Alice Springs.

Detective Senior Sergeant Andrew Barram told the Supreme Court in Darwin he inspected Rolfe's police utility belt after the shooting.

The former officer-in-charge of the NT Police operational safety section found Rolfe's Taser battery was flat.

"It appeared the safety switch had been left in the on position," he said on Monday.

The court has previously heard Mr Walker was unlikely to have been a threat to Rolfe when he shot the teen.

Human movement expert Andrew McIntosh found Rolfe had moved away from Mr Walker before he pulled the trigger for the first time.

"On balance, by the time Rolfe first shot Walker he was unlikely to be a direct threat to Rolfe," he said. 

"Immediately prior to the first gunshot Rolfe was separated from Walker."

However, he said Mr Walker may have been a threat to Rolfe and his partner Remote Sergeant Adam Eberl, then a constable, before he was shot.

This is when the pair was wrestling with Mr Walker as they attempted to arrest him after he had lied about his identity.

During the scuffle Mr Walker stabbed Rolfe in the shoulder and Sgt Eberl struck the teen before placing his right arm around his head and neck while grappling his left arm.

About the same time Rolfe fired his first shot and Sgt Eberl and Mr Walker fell to the ground.

Rolfe remained standing as he fired the fatal second shot and the third shot into Mr Walker from behind Sgt Eberl, who was on top of the teen.

He has pleaded not guilty to murdering Mr Walker, saying he was defending himself and Sgt Eberl from a violent offender.

The Crown has conceded the first shot, which was fired while Mr Walker was standing and resisting arrest, was justified.

But it says the second and third shots, which are the subject of the murder charge, went "too far".

The trial continues.