Homicide police are investigating after a woman's body was found on a Balcatta road in Perth's north.
Police suspect a 48-year-old woman hit by a car and left for dead.
Security cameras captured a group of people one street away about 1am on Wednesday at the same time the body was found.
"Police came across a group of people and a deceased woman on the road," Commissioner Col Blanch said.
"They were in the process of calling police, but police came across it at the time."
Nearby residents woke up to screams and the death sparked a major police probe.
"It was 'help' and just crying and just shouting," one resident said.
Police were forced to close Wanneroo Road to allow homicide detectives to search a crime scene spanning 600 metres.
Major crash and forensic officers also combed for evidence near Nollamara Avenue.
"I know that puts motorists out, but we've lost a life here," Blanch said.
"Someone's lost a family member so we're going to do our job properly."
The woman's death remained a mystery until late in the afternoon, with police saying the investigation indicated she had been hit by a car. No driver has been located.
"Given she was on the road, that would be one of the theories they're working on," Blanch said.
The homicide squad is also going door to door as they hope to catch a glimpse of the car allegedly involved.
Wanneroo Road re-opened after 15 hours of commuter interruption.
