Early yesterday morning, a woman in her 30s was taken from a property in Balcatta, about 10 kilometres from the CBD, to hospital under police guard.
An extensive crime scene set up on Campion Avenue remained in place last night.
The alarm was raised soon after 3am, after it’s understood a six-month-old boy suffered stab wounds.
Multiple ambulance crews rushed to the scene, but there was nothing they could do to save the baby.
The woman in her 30s was also taken to Sir Charles Gardner hospital, accompanied by police.
Forensic officers scoured the scene throughout the day.
Neighbours told 9News they didn’t hear anything this morning, and the first they knew anything was wrong was when they saw the flashing police lights.
The woman has been cleared by the hospital to leave but she remains there under police guard.