Kumanjayi Walker, 19, died on November 9, 2019, after Constable Zachary Rolfe, 31, shot him three times in the remote community of Yuendumu, 290km northwest of Alice Springs.
Aboriginal community police officer Derek Williams said his nephew Mr Walker was in the community to attend a beloved family member's funeral and there should have been no urgency to arrest him.
"He only ran off from (a rehabilitation program). He wasn't a murderer," Mr Williams told the inquest into Mr Walker's death on Thursday.
"He wasn't a big threat. He just wanted attend the funeral."
Mr Williams described his nephew as a shy and slow boy, who liked video games and football.
He said it was an error for Const Rolfe and his team, who had been sent from Alice Springs to relieve exhausted local police, to attempt to arrest Mr Walker on the same day the community was having a funeral.
"You can't just go into people's yard when they're mourning a loss or attending funerals," he said.
"They can't just go in and arrest somebody ... it's no-go, you know.
"They've got to be respectful. We all human beings. We need to be treated as human beings."
Mr Williams said he became concerned when he spotted Const Rolfe's team arrive with a shot gun and an AR15 assault rifle to patrol the community of about 900.
"I thought Yuendumu was going to be a war zone," he said.
"It's only a little community. We are not fighting terrorists. It's really hardcore."
Mr Williams wasn't on duty when Const Rolfe and another officer tried to arrest Mr Walker at 7.21pm.
But he rushed to the home where he had been shot, in disbelief and hoping Mr Walker had only been tasered.
"I didn't go into the house. I just had a peek through the door - blood stains on the mattress and three bullet casings," he said.
Mr Walker died on the police station floor at 8.36pm but the eight officers present didn't tell the community and instead formed a plan to trick them into believing he was still alive out of fear for their own safety.
Outside, the community had gathered, concerned for Mr Walker's welfare as news of the shooting spread through Yuendumu.
Mr Williams was also there and worked through the night to keep people calm as they waited for information, frustrated by the police saying little.
At 10.45pm the officers formed a convoy of vehicles and sped to the airport to meet a plane in an orchestrated ruse to trick the community into believing Mr Walker was still alive.
But the plane wasn't flying Mr Walker to hospital as his family thought.
It was bringing in police reinforcements and evacuating Const Rolfe to hospital in Alice Springs to treat the small puncture wound Mr Walker had inflicted with a pair of scissors during the attempted arrest.
Asked how he felt when he learned his nephew had died long before the convoy drove to the airport, Mr Williams said: "I felt betrayed by my own colleagues and the police force".