Baby fell from car, accused tells court

The man accused of raping and killing a ten-month old baby after taking him from his mother in Broome has said the infant suffered his injuries when he accidentally fell out of a car - and then didn't take him to hospital because he panicked.

Mervyn Kenneth Douglas Bell has pleaded not guilty to murdering and sexually assaulting the baby after taking him from Broome on March 19, 2013.

The 10-month-old baby had suffered horrific injuries from head to toe, including a broken arm and leg and burns on his feet, legs and body.

Today, Mr Bell took to the witness stand to deny the accusations, repeating his claim the baby had fallen out of the front passenger door of his Toyota Landcruiser as he sped away from Broome.

He told WA's Supreme Court that after finding him lying on a grass verge, he did not think his injuries were "that bad".

And Mr Bell said he feared for his own safety if he had taken the injured child back to his mother and grandfather.

Mr Bell gave evidence that the baby suffered the burns on his back in a separate incident after he had fallen out of the car, when he had placed him on hot rocks next to a swimming hole in Karratha.

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.

CCTV footage captured by police showed 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 arrived at the roadhouse at around 1.30pm, when emergency services found the boy dead.

The trial continues.