Autopsy results following what was believed to be the drowning death of a four-year-old boy in regional Queensland have prompted police to open a homicide investigation.

The boy’s death on August 29 near Mackay was initially reported as a suspected drowning in a residential pool, but the scientific findings have led to detectives re-examining the case.

Results indicated “the cause of death was inconsistent with drowning”, Queensland Police said in a statement on Wednesday.

While the cause of death is still unknown, police believe the child died before entering the pool.

Detective Inspector Tom Armitt said the boy lived with his mother and the family had been cooperative with police.

“We’re dealing with the death of a four-year-old boy and obviously a small child … relies heavily on the care of other people,” he said on Thursday.

“His death is treated with the upmost seriousness of any other homicide that we would be conducting.”

The circumstances of “how and why” the boy was found in the pool is under investigation.