Errors in fatal lawnmower crash’s virtual recreation
Rex Martinich |
A ride-on lawnmower accident prosecutors claim was used to conceal a woman’s alleged murder was examined using a computer simulation that contained errors, a jury has heard.
Robert John Crawford is accused of murdering his wife Frances by strangulation at the couple’s property west of Brisbane in the early hours of July 30, 2024.
He pleaded not guilty to murder at his Brisbane Supreme Court trial which began in October.
Ms Crawford’s body was found by paramedics at the bottom of a retaining wall near an overturned ride-on lawnmower after her husband called triple zero at 3.38am and attempted to resuscitate his wife.
Crawford has claimed he was in bed when his wife died from crushing injuries or traumatic asphyxia from being caught under the overturned lawnmower’s steering wheel while moving the machine away from automated lawn sprinklers.
Biomechanics professor David Ackland on Wednesday told the jury it was “very unlikely” the mower would have ended up on top of Ms Crawford following computer crash simulations.
They were unable to recreate Ms Crawford coming to rest 1.8 metres from the edge of the wall if the mower was reversing at the time, as was alleged by police, the jury heard.
“It seems very unlikely to me that the mower could end up directly on top of her,” said Prof Ackland, the University of Melbourne’s deputy head of biomedical engineering.
Under cross examination by defence barrister Saul Holt KC, Prof Ackland accepted the simulation understated Ms Crawford’s height by three centimetres.
“It was rounded down. This is what my post-doc (researcher) did,” he said.
Prof Ackland had help from his student to write the code for the virtual crash simulation, the jury heard.
“Help? You mean write the whole thing?” Mr Holt said.
“Yeah,” Prof Ackland said.
Prof Ackland agreed he did not check the code line-by-line but relied on his student who was “probably the best in Australia” with the software.
The simulation’s wall had a slope of 55 degrees instead of the 60 degrees in Prof Ackland’s report to police.
“Perhaps it was left in from a draft. It does not influence the result whatsoever. I did not consider it significant,” Prof Ackland said.
Police provided Prof Ackland with images and laser scans of the scene, Crawford’s version of events and the wife’s autopsy report to run the simulations and provide an expert opinion, the jury heard.
Police testing found the lawnmower’s maximum reverse speed on concrete was 1.09 metres per second.
Prof Ackland said this was a very slow velocity given the average person walked at 1.3 m/s.
The only virtual scenario where Ms Crawford’s 65kg, 173.5cm-tall body landed 1.8m from the wall involved driving off the edge at the maximum forward speed of 2.4 m/s and with no contact between her head and a rock, the jury heard.
“It was almost like being thrown off at that velocity,” Prof Ackland said.
Ms Crawford suffered an extensive injury to the back of her head which was assumed to have been caused by impact with a bloodstained rock at the top of the wall, he said.
The bloodstained rock was 1.68 metres across from a damaged rock assumed to be a point of impact with the mower, the professor’s report found.
“The deceased could not have been seated in the mower at the time she struck the rock,” Prof Ackland said.
His work involved researching joint function and how the body moves to find advances in sports science, disease and injury treatment and orthopaedic devices, the jury heard.
Under cross examination by Mr Holt, Prof Ackland agreed his doctorate was focused on the human shoulder and not in simulating a body falling from height and coming to rest.
Prof Ackland also agreed there was no lawnmower, rocks or natural deviations in the wall’s slope included in his simulations.
The trial continues.
AAP