A 19-year-old man has clashed with a magistrate on his first appearance in court charged with the murders of an eight-year-old boy, a 15-year-old girl and their 48-year-old mother in Perth’s north-eastern suburbs.

Teancum Vernon Petersen-Crofts was charged after the woman and her son were found dead and her daughter was found critically injured at a house in Ellenbrook, about 30 kilometres north-east of the city centre, in the early hours of Sunday morning.

The teenage girl was taken to hospital but died on the way.

Appearing in Midland Magistrates Court in handcuffs and flanked by two security guards, Mr Petersen-Crofts began talking confusingly over the magistrate.

Referring to a person named “Griff” or “Griffin”, the teenager said “he’s a criminal” who “wanted to take me out bush”.

“He did it and he came back for my family,” Mr Petersen-Crofts said. “I ran away from him and went back home.

He came back for my family. Mama is with me.”

Magistrate Greg Smith asked Mr Petersen-Crofts to stop talking, but he ignored the request and continued with his outburst.

“I was painting a picture of Jesus … Mama told me to save myself,” he said.

“He looks like a serial killer and he’s a security guard.”

Mr Petersen-Crofts was remanded to the Frankland Centre secure mental health facility at Graylands Hospital.

The teenager, who according to police also lived at the house on Brixton Crescent – which according to government records is a state housing property – is expected to appear again in Stirling Gardens Magistrate Court next week.

It is understood Mr Peterson-Crofts is related to the woman and children.

Community in shock over ‘tragedy’

Aliyah Grey and Hunter Turinui-Kaire, two friends of the teenage girl, said the news was hard to take in.

“They had a beautiful family and … they were all so connected,” Aliyah said.

“Her mum was so caring — if you needed anything, like if we needed her, she’d be there as well.”

“I just never would have thought anything like that would happen. Especially to a family like that,” Hunter added.

Police remove a pair of scissors from the Brixton Crescent home. Photo: ABC

“My little brother would always hang out with [the eight-year-old boy] and they were pretty close, and he was devastated as well.”

Neighbours said they had heard loud aggressive disturbances from the home on a few occasions in the past six months.

But they said, for the most part, the area was relatively quiet and the mother and younger children at the house were always friendly and polite.

One neighbour mentioned how the eight-year-old boy would smile and wave whenever he walked past her home.

Another said she spoke to the woman and her son from time to time and had been left “shaken” by their deaths.

“Unfortunately this tragedy has left us speechless and we have no information as to what has happened,” she said. “Our prayers and hearts go out to the family.”

WA Deputy Premier Roger Cook said the community needed to “wrap its arms” around the family and friends of the victims.

“Out of these sort of tragic circumstances you at least want to see some lessons, you want to understand the circumstances behind it, put in place policies that can better respond to it,” he said.

A ‘complex’ crime scene

Officers went to the house after they were initially called to a convenience store on The Broadway at 1.30am on Sunday.

Police allege Mr Petersen-Crofts had entered the store and asked staff to call police.

They then investigated the property and found the two bodies, and the teenage girl outside the house fighting for her life.

Brixton Crescent was soon cordoned off as the homicide squad and forensic investigators began what was described as a “complex” inquiry.

Later on Sunday morning, officers found a large pair of scissors lying in a verge garden bed about 30 metres from the house.

Investigators photographed the scissors before placing them in an evidence container and removing them from the scene.

A dog was later collected from the property and taken away by local council workers.

Police were called to a home near the corner of Brixton Road and Ashburton Street in Bentley just before 4.30pm on Thursday. Photo: AAP

WA Police Assistant Commissioner Paul Steel said on Sunday the deaths would send “shockwaves” throughout the WA community.

“This is a terrible tragedy for the family involved, for their extended family and for those first responders who were forced to attend what was a horrific crime scene,” he said.

“A senior homicide squad investigating officer said to me it is potentially the most horrific crime scene that he has ever been called to.

“My heartfelt condolences go out to all of those who’ve been affected by this tragic incident.”

The house remains cordoned off and police are expected to remain at the scene for some time as part of their investigation.

-ABC