The badly damaged vehicle was lifted from the river by helicopter and examined by police yesterday.
Acting Sergeant Blair Duffy said the handbrake was on and it was in gear.
"The question is, was the vehicle turned off or not?"The Ace Rental Cars Nissan Bluebird was parked by a British woman, aged in her 60s, and her daughter, from Auckland and aged in her 30s, on Oxenbridge Tunnel Rd, at the intersection with Gorge Rd, next to the Edith Cavell bridge on Saturday, about 5pm.
Constable Logan Dickie, of Queenstown, said the women took their camera and were walking towards the bridge when they heard a crunch and thought a Shotover Jet boat had crashed.
Debris and personal effects were strewn on a rock ledge below where the car had hit before it fell into the fast-flowing river.
The women [went] back to where they had parked the car and found it missing.
They ran over to the Shotover Jet facility to advise people there was no-one in the car, Const Dickie saidThe women were "not injured but extremely shaken up", he said.
Police had not established yet why the car had rolled off the hill.
The women were "not sure" if the handbrake was engaged and it would be determined once the car was fully examined, he said.
Shotover Jet staff manoeuvred a jet-boat to attach marker buoys to the submerged car.
A digger, crane and a helicopter were considered for retrieving the car.
The scene attracted a crowd of more than 30 people on the bridge until police officers cleared the structure and closed it to traffic at 7.15pm.
A Heliworks helicopter hoisted the car to an inlet where it was salvaged.
The bridge reopened at 7.45pm.
Queenstown firefighters also attended and St John Wakatipu was called but stood down when it was determined no-one was injured.
"Our inquiries are continuing and we'll decide if charges will be laid and if they are liable for any costs incurred," Const Dickie said.
Louis-Philippe Thiffault, a tourist from Montreal and based in Dunedin, said: "I heard a big bang and everybody started yelling `the car's fallen down the cliff'.
Some people reckoned they saw people in the car and started to worry.
"`The owner of the car came running, worried the car landed on a [jet] boat, and told people nobody was in the car and not to dive for it."
Shotover Jet boats were not operating when the car landed in the river.
The mother and daughter declined to comment.
