A mother has been charged with murdering a seven-month-old boy in what police alleged was a domestic violence homicide.
Detectives are investigating the baby's death at a home in Balcatta in Perth after emergency services were called to the property about 3am on Monday following reports of a serious assault.
It is believed the infant suffered stab wounds.
Multiple ambulance crews arrived at the address where they found the baby with critical injuries.
The boy died at the scene.
A 31-year-old woman was taken to Sir Charles Gairdner Hospital and a 13-year-old female teenager transported to Perth Children's Hospital.
The death was being treated as a domestic violence homicide confined to the family, WA Police Commissioner Col Blanch said.
"As you can imagine, this is something a trauma that no one would ever recover from, and I think the family just deeply affected," he told reporters on Tuesday.
He said family members were present at the time of the baby's death.
"There was a male, a female and a young person," Mr Blanch said.
The police commissioner described the baby's death as a "very sad story".
"There would be very few cases where you would have a crime scene of such a horrific nature for our officers and all first responders involved," he said.
"And certainly those officers would be entitled to their critical incident leave, but that's something that will most likely haunt them for the rest of their careers."
Family members of the infant were assisting detectives with their inquiries, police said.
The woman will appear before the Perth Magistrates Court on Wednesday.
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