Detectives were last night questioning a man over the stabbing death of an 18-year-old man in Noranda.
The victim was stabbed once in the chest during an altercation at his home in Widgee Road about 10.30am yesterday.
Police and paramedics were called and the man was taken to Royal Perth Hospital but efforts to revive him failed.
Det-Sgt Cameron Blaine, of Mirrabooka police, said a 24-year-old man was arrested at a home in Bedford yesterday afternoon and was helping police with inquiries.
Det-Sgt Blaine said the man was known to the victim and several other people had been at the home at the time of the stabbing.
But he would not reveal the relationship between the men.
"Police are conducting inquiries in relation to witnesses," Det-Sgt Blaine said.
"There are several people yet to be spoken to."
Forensics officers were analysing the crime scene and were expected to remain at the home well into the night.
A young woman who arrived at the scene yesterday was visibly upset. It is unclear what her relationship was with the dead man.
No charges had been laid over the stabbing last night.
Widgee Road remained closed to all but local traffic last night.
Det-Sgt Blaine said the victim's family had been told of his death.