UPDATE: 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, clashed with the judge 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".
It is believed that the accused is related to the victims.
EARLIER: A TEENAGER has been charged with the "horrific" killing of a mother and two children at their home in Western Australia yesterday.
Disturbed police officers said the bloody crime scene was the worst they have ever been to after making the grim discovery at a house in Ellenbrook - about half an hour northeast of Perth.
As they opened the door, officers saw a boy and girl dead inside and another female in the backyard suffering from critical injuries.
An ambulance was called to the scene and the female was taken to Royal Perth Hospital.
However, she died just a short time later.
Police said the deceased are believed to be a mother, as well as her young son and daughter.
Now, a 19-year-old man has been charged over the sickening crime.
Cops say the teenager is understood to have lived with the victims, but his relationship to them remains unclear.
Police officers are also understood to have found a large pair of scissors about 30 metres from the house.
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.
"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."
Police would not confirm the ages of the victims.
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.
According to the ABC, a male had entered a nearby 7-Eleven store, and requested police attendance.
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."