If a 10-month-old baby had fallen out of a moving car as claimed by his accused murderer, he would have suffered more extensive injuries, a forensic expert has told a trial in Perth.
Mervyn Kenneth Douglas Bell, 27, is on trial in the West Australian Supreme Court accused of murdering and sexually assaulting the Broome child in March last year, including inflicting third-degree burns and bruises on the boy over about 15 hours.
Bell claims the child's injuries were caused when he fell out of a moving car travelling at about 60km/h, when the boy sat on hot rocks by a river, and when he fell into the water.
Forensic pathologist John Hilton gave evidence on Tuesday that abrasions on the child's leg were consistent with falling out of a car, but under cross-examination, admitted he would have expected to see more extensive injuries.
The defence witness said hot rocks could also have caused some of the "thermal injuries", but not the scalding on the boy's lower back.
Professor Hilton said that injury was consistent with hot water on the skin.
While the exact cause of the baby's death could not be determined, Professor Hilton said hyperthermia, or the over-heating of the body, could be a possible cause.
After the court heard Bell had not slept for about 24 hours before the incident, sleep disorder specialist Scott Claxton said the accused's decision-making and judgment could have been impaired.
In her closing address, prosecutor Amanda Forrester said Bell had been a "dishonest" and "utterly unconvincing" witness with a version of events that were "highly improbable".
She said Bell had showed "complete and utter indifference" towards the baby.
The judge-alone trial continues.
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