A baby boy suffered five fractured ribs, a lacerated liver and a bruised heart before dying from internal bleeding in 2004, police have revealed.
Eleven-month-old Dylan Robert James Lindsay was found dead at a home in Port Lincoln, with detectives believing he was assaulted by an adult.
"This certainly wasn't someone who has fallen out of bed or down some stairs."Detective Brevet Sergeant Mathew Bengel
Two people were arrested over his death but the case was later dropped.
Detective Brevet Sergeant Mathew Bengel said police had decided to release details of the boy's injuries in the hope it would prompt people with information to come forward.
"I hope it sparks the conscience of someone in the community and prompts a change of heart about speaking with us," he said on Wednesday.
Medical examiners believe Dylan would have taken about six hours to die.
They also found his abdomen and chest were covered in texta marks in an attempt to cover up 18 bruises found on his body.
"I believe he was assaulted by an adult. This certainly wasn't someone who has fallen out of bed or down some stairs," Sergeant Bengel said.
Before his death, the boy had been left in the care of his mother's cousin and the cousin's partner.
They remain persons of interest.