WA's top cop disturbed by baby death case

Police who conducted an interview with a young father accused of killing his baby son that was so flawed it caused his charge to be dropped are being investigated and may face disciplinary action.

Dylan Clinton O'Meara, 23, was charged with manslaughter after his seven-month-old son Shisui-Grady George O'Meara was found dead in his cot, with broken bones, at their Rockingham home in April 2016.

But prosecutors dropped the charge in the West Australian Supreme Court on Thursday after Justice Lindy Jenkins ruled in December one of two police interviews was inadmissible.

Mr O'Meara revealed he had an imaginary friend named Alex, who detectives urged him to speak with to find out how the baby died.

They also conducted the second interview while he was tired and hungry.

Police commissioner Chris Dawson said the interview had not gone "entirely right" but no-one had yet told him the conduct was unlawful.

He said Mr O'Meara had some obvious vulnerabilities.

"Clearly this case should disturb us all," Mr Dawson told 6PR radio on Friday.

The detectives are being investigating by acting commissioner Gary Budge.

Mr Dawson said police were still seeking justice for the baby, which could include Mr O'Meara being charged again.

Mr O'Meara had been accused of lifting the baby out of the cot by pulling him by the arm, which caused his foreman bone to break. The infant also had two other fractures.

He then allegedly placed part of a blanket into the baby's mouth in an attempt to settle his crying and provide something to bite down on.