SYDNEY - John Sharpe told police he had fantasised about killing his New Zealand-born wife Anna Kemp for months before he shot her with a spear gun.
Sharpe's interviews with police have been released to the Sunday Sun-Herald newspaper.
He was jailed last year for a minimum 33 years for the 2004 murders of Ms Kemp and their 19-month-old daughter Gracie at their Mornington, Victoria, home.
He told police that Ms Kemp, who came from Dunedin, was asleep when he shot her, but his daughter looked at him before he killed her.
In his only explanation for the horror, Sharpe said that after fantasising about killing Ms Kemp for months, "a madness" then took over him.
On the day of the crime, he thought about the murder for about 30 minutes, then took a spear gun from his garage.
"You know what you're doing is sort of insane, but there's just this weird part of you that's almost unstoppable or something," Sharpe told police.
"You're almost like on automatic pilot sort of thing.
"I can't really remember much of what I thought of - of anything. Just apart from the sort of crazy sensation ... it was totally emotional."
He shot Ms Kemp twice in the head and left her body in their bed. A day later he buried her in a shallow grave in their backyard.
He said that for the next four days voices in his head debated Gracie's fate.
"It was sort of in and out of my head all week - I could hear things going through my head ... the voices saying, 'You can't do it, you can do it, you've got to do it' ... every option was coming up.
"I was thinking about taking care of Gracie by myself and just among all this madness - that's when I lost the plot."
He took Gracie with him when he bought the spear he would use to end her life.
He said her death was not instant.
"It's shocking. It's all shocking. I know that it didn't kill Gracie because she started screaming," he told police.
His wounded daughter looked at him when she awoke and began to scream. As he fumbled to finish the killing, he was unable to look at the toddler.
The interview revealed he had scrawled notes as he formulated his cover story for the murders.
He pretended Ms Kemp had run away with another man.
Sharpe would not admit to the murders for three months and confessed only after police told him he would be charged.
The newspaper said he wept like a baby on hearing he would be charged.
- NZPA
Killer speaks of fantasies before murdering wife
John Sharpe killed his wife Anna Kemp and, four days later, their daughter Gracie.