The body of missing health worker Gayle Woodford is believed to have been found buried in a shallow grave outside a remote South Australian town.
Superintendent Des Bray said a body had been found on Saturday afternoon, after Ms Woodford was reported missing on Thursday morning.
"Our worst fears were realised. We found a shallow grave on the roadside about a kilometre and a half out of Fregon," Supt Bray told reporters on Saturday.
"We believe the grave will contain the remains of Gayle."
The 56-year-old health worker's ambulance was also allegedly stolen on Thursday morning, and police have charged a 36-year-old Fregon man with theft of a motor vehicle and driving while unlicensed.
Forensic investigators will leave Adelaide on Sunday morning to examine the body at the scene, which is under police guard, on APY lands.
Supt Bray said Ms Woodford's family would be "completely devastated" by the news.
"As are many of the people in the community because Gayle, I'm told, was a much loved person here, so this is devastating news not just for Fregon but for the whole APY community," he said.
Ms Woodford normally drove the local ambulance and its GPS data shows it left Fregon shortly after midnight on Thursday and travelled to Mimili.
In the early hours of Thursday morning, the ambulance travelled via Indulkana to Marla, arriving around daybreak.
Police intercepted the ambulance in Coober Pedy at 10.30am and two men and a woman inside were interviewed.
"We only have one suspect and that suspect is in custody on vehicle-related crimes," Supt Bray said.