Homicide detectives are investigating the death of a one-year-old baby boy in Golden Bay.
Police attended a residence in Golden Bay on Sunday following the death.
It is understood the same baby was allegedly assaulted in Narrogin in October last year.
The then six-week-old was taken to Narrogin Regional Hospital before being transferred to Princess Margaret Hospital.
He was later released.
A 25-year-old man from Mandurah was charged with grievous bodily harm over the alleged attack.
The investigation into the boy's death is ongoing.