Queensland police officer gets nine years jail for killing baby son

A Queensland police officer who fatally punched his infant son with such force it pulped his liver has been sentenced to nine years' jail.

The 10-week-old was sitting in his rocker chair on June 28, 2014 when Colin David Randall delivered the blow.

He suffered fatal injuries and couldn't be revived.

After realising the damage he had inflicted, the Brisbane Supreme Court on Friday heard the former senior constable phoned his wife and said their son "had gone limp and lifeless and he was not breathing".

It was the start of a lie that he would maintain until last month when, three days before his murder trial, he pleaded guilty to a lesser charge of manslaughter.

Justice Peter Davis delivered a scathing assessment of the 41-year-old in sentencing, saying his plea did not reflect genuine remorse.

Justice Davis said he believed the reason why Randall lied about what he had done was the same as why he finally admitted killing his son.

"Your motivation is self-preservation," he said.

"Manslaughter seems to have been the best outcome you could have hoped for in a trial."

Justice Davis said while he accepted Randall's decision to punch his son was spontaneous, it was "very deliberate".

"It was a forceful punch delivered to the abdomen of the baby, which pulped his liver," he said.

The court heard there were no significant factors that led to his violent outburst.

Justice Davis described the frustration he was feeling at home as "normal domestic pressures".

He said the stress caused by his extra-marital affairs were matters of his own making, although he took into account the fact he was experiencing bullying at work.

Randall was sentenced to nine years' jail.

Justice Davis ordered he serve five years of that behind bars, where he will remain in solitary confinement because of the dangers he faces from other prisoners as a police officer and child killer.

After time already served, he will be eligible for parole on January 30, 2021.