A 24-year-old woman with stab wounds was located in a car boot in Berrima on Wednesday February 3.
She was treated at the scene and taken to Liverpool Hospital.
Police received a triple zero call at approximately 11:30am by an observant motorist who reported seeing a hand waving from the rear taillight section on a white Holden Commodore sedan on the Hume Highway near Pheasants Nest.
Highway Patrol Officers attached to the Southern Traffic Group stopped the vehicle on the Hume Highway in Berrima at approximately 11:50am.
Detective chief inspector Brendan Bernie said police were exploring all lines of enquiries.
"An 18-year-old female that we will allege as the driver of the commodore and a 24-year-old female passenger were arrested and taken to Southern Highlands Police Station," he said.
"The 24-year-old female that was located in the boot of the car was treated for a stab wound to the knee, thigh and forearm and was conveyed to hospital.
"She is currently undergoing treatment for those injuries. They are not considered life-threatening and she's in a stable condition, assisting police with enquirers."
Inspector Bernie said the two other females were yet to be interviewed by police and were assisting police enquiries. No charges have been laid.
"Early indications suggest that it started possibly in the Campbelltown area but that is still yet to be confirmed. It's subject to our ongoing enquiries," he said.
Inspector Bernie said he had not received information about how she got her hand through that cavity or how long she had been in the boot.
"It's certainly a line of enquiry that we are looking into," he said.
Inspector Bernie said the relationship between the three women is not currently known and that was part of the ongoing enquiries.
"Unfortunately we haven't interviewed all the parties yet," he said.
Police also praised the motorist who made the initial triple zero phone call.
"Some excellent work was done by the motorist that identified a hand coming out the vehicle," Inspector Bernie said.
"They subsequently notified the police and we can't thank the motorist enough for their assistance.
"As a result, a highway patrol officer positioned themselves in the path of the vehicle in the direction it was travelling and fortunately they located that vehicle and conducted a vehicle stop.
"It was excellent police work and we are fortunate that we found this lady alive.
"We are thankful this ended with no loss of life and with no one seriously injured."
Police believe the 24-year-old victim was in the boot of the car for some time but could no speculate for how long. Inspector Bernie said he hadn't had the opportunity to be briefed on what she said to police.
"It will no doubt come out in subsequent interviews," he said.
"We believe the incident happened this morning (February 3) but at exactly what stage she was put into the vehicle or entered the vehicle is still under investigation."
An investigation into the circumstances surrounding the incident is underway and a forensic search of the car is yet to be done.
Anyone with information that may assist investigators is urged to contact Crime Stoppers: 1800 333 000 or https://nsw.crimestoppers.com.au. Information is treated in strict confidence. The public is reminded not to report information via NSW Police social media pages.
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