Father admits murdering baby son

A father once jailed for breaking his baby son's arms and legs has pleaded guilty in the Supreme Court to murdering another of his children - a four-month-old boy - in similar circumstances.

John Patrick O'Kane pleaded guilty this morning during a quick court appearance. He will be sentenced on February 2.

O'Kane was charged in January after leading detectives to a shallow grave near Collie where the body of Zach O'Kane had been dumped after being kept in the boot of a car for several days.

The 41-year-old's guilty plea to the murder means his history of violence - including seven convictions in 1994 for blinding his baby son in one eye and fracturing all his limbs - can be made public for the first time.

_The West Australian _ has learnt that O'Kane was sentenced in NSW to six years jail for committing grievous bodily harm to another son, who was six months old at the time.

Medical evidence presented to the NSW Supreme Court showed that the infant had been punched, shaken and twisted violently by his father while living in a Cronulla caravan park with the baby's mother.

There were breaks to the infant's upper and lower right arm, lower left arm, ribs and both legs. An injury to his left eye had caused blindness.

"(His) injuries are almost unquestionably due to abuse and neglect and took place over a period of at least a month," the court documents say.

"One of the eye injuries was most likely caused by a direct blow to the globe of the eye."

O'Kane, an unemployed truck driver, returned to WA after serving his jail sentence for the assaults and started a family with his new partner.

Four months after baby Zach was born, O'Kane disappeared with the child from their Hillman home, sparking a police manhunt.

He was found sitting in a car near Pinjarra with a self-inflicted injury to his arm.

Zach's body was found in Wellington National Park, 200km south of Perth, the following day.

According to post-mortem examination results, the baby had suffered several fractures, including broken ribs, before his death.

Since being arrested in January, O'Kane has spent time at Graylands Hospital undergoing a detailed psychiatric assessment.

In August, he told a court he wanted to plead guilty to the manslaughter of baby Zach, but the offer was rejected by the Director of Public Prosecutions.

After being charged for the 1994 assaults, O'Kane told psychiatrists he was ashamed of what he had done and suggested that the death of another of his children, Adele, from a medical condition had left him depressed and dependent on alcohol and drugs.

Adele was also four months old when she died.

In a report by one of the psychiatrists in the 1994 case, O'Kane was found to have an "immature personality" and an inability to cope with any emotional distress.

But the psychiatrist concluded he was "certainly not a violent psychopath."

O'Kane's lawyer Terry Dobson said he would not make any comment about the case until after today's hearing.