A WA Police officer who fatally shot an unarmed man at a house in Perth's north-eastern suburbs last year will not be charged over the death.

Key points: Ly Tong died after the officer shot him three times as he emerged from a bedroom

Ly Tong died after the officer shot him three times as he emerged from a bedroom Police say Mr Tong was not holding a knife as reported, but appeared "quite quickly"

Police say Mr Tong was not holding a knife as reported, but appeared "quite quickly" The state coroner will review his death and a public inquest is expected to be held

An internal investigation was launched by police after Ly Tong, 38, was shot dead when officers went to the house in Beechboro on November 22 in response to a family violence incident.

WA Police Commissioner Chris Dawson said officers had been told Mr Tong was armed with a knife or something similar and had threatened to kill his mother and attack police.

He said two officers entered the house on Yenisey Crescent and found the elderly woman and two small children "in a confined space", with Mr Tong in a separate bedroom.

Ly Tong had a family violence restraining order out against him at the time of his death. ( Supplied: Family )

When Mr Tong emerged from the bedroom, he was shot three times "within seconds" by one of the officers and died almost immediately.

Commissioner Dawson said Mr Tong did not have a weapon in his hands, but was found to have a small knife in his pocket and four other knives in the bedroom.

He said the police officer who fired his gun had been forced to make "a split-second decision".

"The outcome of the investigation is that police concluded there were no reasonable prospects of convicting the police officer for causing the death of this man," Commissioner Dawson said.

"I am satisfied that this has been a very thorough investigation into what was really a very tragic death.

Family members were left shocked and seeking answers after Mr Tong was shot dead. ( ABC News: Sarah Collard )

"The man was not armed with a knife at the time he came out of the bedroom.

"What I will say is that he emerged from that room quite quickly, and the officers were faced with a very split-second decision."

'My brother didn't deserve to die'

Mr Tong's sister, Oanh Tong, said the family was not satisfied with the Commissioner's response, and could not understand why police had not used pepper spray or a taser to subdue her brother instead of shooting him.

"I want justice for my brother," she said.

Oanh Tong says her family is still mourning the loss of her brother. ( ABC News: Madeline Palmer )

"No knife, no weapon. Still got three shots, which my family doesn't understand — my brother didn't deserve to die."

She said the family was still grieving.

"I still cry every day and when I'm at work I keep thinking about my brother," Ms Tong said.

"I'm missing him hanging around the house."

She said the family planned to engage a lawyer to examine their legal options.

Officer followed his training: Dawson

Commissioner Dawson said the officer responsible for the shooting had previously been involved in two similar situations where he had been confronted by someone with a knife and had been forced to draw his firearm.

But he said he had not fired his weapon on either previous occasion.

WA Police Commissioner Chris Dawson says the officer has returned to partial duties. ( ABC News: James Carmody )

Commissioner Dawson said the officer had served for "about five or six years" and had only recently been re-trained in critical skills training.

"The officer that fired the shot was of the belief that the person was armed," he said.

"He's experienced, he was accompanied by a sergeant who is very experienced.

"I'm satisfied that the officer who fired the shots and the other officer attending did exactly what their training teaches them to do."

Commissioner Dawson said a family violence restraining order was in place against Mr Tong at the time of the incident, and he was in breach of the order by being at the house.

Police had previously revealed he was well known to them, saying officers had gone to the house numerous times.

Mr Tong's death has now been referred to the state coroner and Commissioner Dawson said he expected an inquest would be held.

Police launched an internal investigation after the fatal shooting. ( ABC News )

He again offered his condolences to Mr Tong's family and said they had been informed of the outcome of the investigation.

He said the officer who fired his gun had returned to "stand-aside duties" after being stood down in the wake of the shooting, and was undergoing "reassimilation" before his return to full-time frontline duties.