One of Australia's leading pathologists has said he would have expected to see different injuries on the body of a 10-month old baby, who his alleged killer claimed fell out of a moving car.
Mervyn Kenneth Douglas Bell, 27, has pleaded not guilty to murdering and sexually assaulting the baby after taking him from his mother's house in Broome on March 19, 2013.
The infant had suffered horrific injuries from head to toe, including a broken arm and leg and numerous burns on his feet, legs and body. The boy also had severe injuries to his genitals and anus.
Mr Bell is accused of intending to kill the baby and inflicting injuries on the child over a 15-hour period before he sped into the Fortescue River Road House with the boy's lifeless body in his arms.
But he claims the boy received the injuries after falling out of a car while it was moving around 60kmh, and was then burned later, when he was placed on hot rocks by the side of the river.
Professor John Hilton, who worked on the first Bali bombing and the Victorian 'Black Saturday' bushfires, was called in by the defence as an expert witness.
Despite his decades of experience, Professor Hilton said the baby's injuries were of a diversity he had "seldom if ever seen".
And under cross examination, he admitted if the child had fallen out of a moving vehicle, he would have expected to see more extensive and different injuries.
Earlier in his evidence, Professor Hilton said a huge abrasion down the entire length of the child's right leg was consistent with falling out of a car. And he said some of the deep, red burns on the child could have been caused by hot rocks.
He also said some of the other burns on the child appeared to be scalding, from hot liquid, and others possibly caused by having a hot, tubular object applied to the skin.
He agreed with earlier evidence from other experts in the trial, which said the actual cause of death of the boy was "unascertainable".
Defence lawyer John Myers also suggested to the professor that the brain swelling found in the child could have been caused by hyperthermia, or overheating of the body.
CCTV footage captured by police showed Mr Bell buying groceries and cigarettes at 9.50am on the morning of the boy's death, and then buying a six pack of beer around two hours later.
He had left the baby in the car while he shopped, as temperatures in Karratha reached soared to nearly 40C.
He arrived at the roadhouse at around 1.30pm, when emergency services found the boy dead.
The trial continues.