THE teenager accused of the murder of an eight-year-old boy, his sister and their mother in Perth’s northeast has made a bizarre outburst in court.

Teancum Vernon Peterson-Crofts, 19, defied a judge’s warning not to speak when he appeared without a lawyer in Midland Magistrates Court today to face three murder charges.

Mr Peterson-Crofts looked around the public gallery before sitting down and saying “a criminal wanted to take me out bush — he did it and he came back for my family”.

The magistrate told him he didn’t need to say anything but he replied: “I have to ’cos mamma is with me.”

The magistrate ordered him to be sent to a psychiatric centre due to concerns over his mental health.

Mr Petersen-Crofts interjected: “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.”

Mr Petesen-Crofts then told a security guard standing by his side that he looked “like a serial killer”.

The identities of the three victims, who are understood to be related to the accused, have been revealed .

Michelle Petersen, 48, and her daughter Bella, 15, and Rua, 8, were killed in their family home on Brixton Crescent in Ellenbrook, on Sunday morning.

Disturbed police officers said the bloody crime scene was the worst they had seen after making the grim discovery at the house, which is about 30 minutes’ drive northeast of the Perth CBD.

As they opened the door, officers saw a boy, 8, and his mother, 48, dead inside, while the boy’s sister, 15, was in the backyard suffering from critical injuries.

An ambulance was called to the scene but the injured teenager died on the way to Royal Perth Hospital.

Police officers are also understood to have found a large pair of scissors about 30 metres from the house.

The 19-year-old suspect was arrested, taken into custody and questioned before being charged.

He is understood to have lived with the victims, but his relationship to them remains unclear.

Police say he walked to a nearby 7-Eleven store in the early hours of Sunday morning and asked the shop attendant to call 000.

When police officers arrived at the store, the teenager is alleged to have led them to the house where the bodies were discovered.

On a fundraising page to raise money for the family’s remaining children, a friend wrote that the deceased mother was “kind, happy and loved her kids, all of them unconditionally”.

“At times in her life she was rough.” she wrote. “She was flawed, but we all are. No-one is perfect and [she] tried. She was always good to me, always supported me, always made me feel like a better person.”

Assistant commissioner Paul Steel told reporters in Perth the disturbing discovery had shaken his colleagues.

“A senior homicide squad investigating officer said to me today it is potentially the most horrific crime scenes he has ever been called to,” he said yesterday.

“They located two deceased people inside the home and a further victim in the rear yard.

“An ambulance was called in relation to the critically injured victim in the rear yard who was conveyed to Royal Perth Hospital and, tragically, she died en route.”

He added it could take days for the scene to be processed.

Police were initially called about 1.30am on Sunday to a convenience store on The Broadway before they went to the home. Both are still being processed as crime scenes.

“The home, along with the convenience store, is now a crime scene,” Mr Steel said.

“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.

“I can assure the community that WA Police are applying all resources that we can to get to the bottom of what’s happened here.”

A man who lives in a neighbouring street earlier told ABC he was woken by screaming and yelling about 1am.

“I just heard a lot of screaming and yelling and a bit of fighting, and the cops flew past here and headed up this way,” Mr Shreck said.

“It was real loud yelling and screaming. It sounded pretty bad. It sounded like a man.”

Mr Steel said while details were still emerging, he believed the incident would have a massive impact on the victims’ families and the WA community.

“At this particular point in time there’s a very complex, and I would say horrific crime scene in place, and it will take us some time to process that crime scene, and that could be days,” he said.

“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. My heartfelt condolences go out to all of those who have been affected by this tragedy.”

A friend close to the family told news.com.au they do not want to speak publicly about the incident at this point in time.

Peterson-Crofts appeared before Midland Magistrates Court on Monday to face three murder charges today.

He will face Stirling Gardens Magistrates Court next week.