Ellenbrook deaths: Woman and two children killed at Perth home

The teenager accused of killing his mother and two siblings has been sent to a psychiatric facility after a bizarre court appearance.

Teancum Vernon Petersen-Crofts, 19, appeared at Midland Magistrates Court this morning over the murder of Michelle Petersen, her 15-year-old daughter Bella and eight-year-old son Rua at their Perth home.

Mr Petersen-Crofts claimed another person was responsible for the attack and said he was punched in the head while painting a picture of Jesus. 

"A criminal wanted to take me out bush - he did it and he came back for my family," Mr Petersen-Crofts said.

The magistrate told him he didn't need to say anything, but he replied: "I have to 'cos mamma is with me".

After the magistrate said Mr Petersen-Crofts would be sent to a psychiatric facility as there were concerns for his mental health, Mr Petersen-Crofts said: "I was painting a picture of Jesus and stayed there for two months".

"He punched me in the head so hard. I left because I had to. I was that scared he was going to kill me.

"Mamma told me to save myself".

He was remanded to the secure Frankland Centre unit at Graylands Hospital and will face Stirling Gardens Magistrates Court next week.

The three bodies were found in a "complex and horrific" crime scene in the Brixton Crescent, Ellenbrook, in the early hours of yesterday morning. 

Police were called to a nearby 7-Eleven convenience store at 1.30am, where they arrested Mr Petersen-Crofts.

Officers were then directed to a nearby house where Ms Petersen and her son Rua were found dead. 

Bella was found critically injured in the backyard of the property and was transported to Royal Perth Hospital, but died in the ambulance. 

A sibling of slain children told TVNZ Rua and Bella were much loved by their mother. 

"He was like a blessing to my mum, he really was," Tamika Petersen said.

"An awesome kid.

"And Bella, she was wicked you know.

"They were both of mum's babies." 

Police were seen taking a pair of scissors from the home yesterday afternoon.

"At this stage it is a very complex and horrific crime scene. It will take us some time to process," Assistant Commissioner Paul Steel said in Perth yesterday.

Asst Comm. Steel said it could take days for the scene to be processed.

"It is a very complex and I would say horrific crime scene. It will take us some time to process, and that could be days," he said.

"It's a crime that I know will send shock waves throughout the community of Western Australia.

"This is a terrible tragedy for the family involved and for the first responders who attended the horrific crime scene."

He said a senior homicide detective confided to him that the scene inside the Ellenbrook home was "potentially the most horrific crime scene (he had) ever attended."

A man who lives nearby street told 9NEWS he was woken by screaming and yelling about 1am yesterday.

"Just heard a lot of screaming and yelling, bit of fighting then a few moments later the cops flew past down there, ended up this way," neighbour Matthew Schreck said.

Police were tight-lipped about the incident before speaking to reporters.

"It's a crime that I know will send shock waves throughout the community of Western Australia," Asst Comm. Steel said

"I can assure members of the the community that WA Police are applying all the resources that we can to get to the bottom of what has happened here."

It comes after another tragic domestic incident in Western Australia where Margaret River man Peter Miles murdered six family members before taking his own life in May this year.