A mother and her two children are believed to be the victims in what police are calling a 'horrific' crime in suburban Perth.
Police said a male and a female were found dead inside a home in Ellenbrook and another woman was found critically injured in the backyard. She died en route to hospital.
A 19-year-old man who lived with the victims at the house has been arrested and is now assisting police with their inquiries.
Police have not yet released the ages of the victims, but it's believed the deceased is a mother, her young son and daughter.
Forensic officers remain at the scene as part of the investigation.
Police said they were called to a convenience store, believed to be a 7-Eleven, on The Broadway in Ellenbrook after a man arrived and requesting police.
Officers arrived at the convenience store and said that after further inquiries went to a nearby home in Ellenbrook.
WA Police say two people were found dead at the scene. A third died a short time later. Source: AAP
"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," Assistant Commissioner Paul Steel said.
"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.
“There is 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.
“What I can tell you is that a senior Homicide Squad investigating officer said to me today that it is potentially the most horrific crime scene that he has ever been called to.”
According to ABC News, police photographed a large pair of scissors lying in a verge garden bed about 30 metres from the house before placing them in an evidence container.
A man who lives in a neighbouring street has told the West Australian he was woken by screaming and yelling about 1am.
"It was real loud screaming and yelling, it sounded pretty heavy," Matthew Schreck said.
Another neighbour said she had just gone to bed about the same time when she heard somebody running past her home.
She said she did not think the noise was unusual at the time.
Anyone with information about the incident should contact Crime Stoppers on 1800 333 000.
