Police say even Usain Bolt would have struggled to jump out of a car travelling at 45km/h as it headed towards the edge of a cliff.
The comment was part of evidence being given at a coronial hearing into the disappearance of Mike Zhao-Beckenridge and his stepfather John Beckenridge, who have been missing for eight years.
From cliff edge into the swell of Blue Cod Bay in a matter of seconds.
Police calculated the vehicle would have been travelling about 45km/h when it went over the cliff. Tyre marks show where it braked briefly near a stake in the ground.
"There had to have been someone in that vehicle, pushing the brake pedal to affect a braking action to cause that evidence," serious crash expert Senior Constable Kenneth Patterson said.
Police say the stake in the ground was a marker to direct the car into water rather than nearby rocks - a murder-suicide.
But the family believes the stake was also marking an escape point for the Beckenridges.
Snr Const Patterson told the Coroner's court the latter scenario would have been difficult.
"Usain Bolt holds the world record for speed at 37km/h and he does it under 10 seconds. It would be unlikely if not impossible that anyone could assume 40-50km/h an hour," he said.
And if he tripped and fell he would have slid 26.55m - a far greater distance than the marker was from the cliff edge.
"If we use that as the spot to alight from the vehicle, they would have insufficient distance and would have gone over the cliff."
Mike's family believe John staged a murder-suicide and the pair are living overseas with fake identification. An Interpol alert would have prevented the pair from leaving the country legally; the family believe they may have escaped on an ocean-going yacht.
There is no monitoring system of the comings and goings of yachts - it's up to the sailor to notify Customs.
