He argued a pathologist during the trial misdirected the jury into believing he stabbed Mrs Gotingco when she was conscious because she was found with blood in her lungs.
Mr Robertson said when asked the cause of death, the pathologist answered with "I guess", "probably" and "I think".
"If pathologist isn't sure, how can the jury be sure," he said.
"Pathologist's opinion cannot be relied on."
Mr Robertson said "she remained unconscious" and believed she had died from her injuries.
He admitted he was "completely off his face" when he ran her down in his car.
But in the trial, the jury was directed to believe Mr Robertson wasn't "too drugged to know what I was doing".
"I smoked drugs all morning and hours before coming into contact with the victim," he said.
"I accept I f****d up."
But he said he didn't murder her.
"At the time I made a very bad decision," he said.
"I was incapable of forming rational thoughts."
He also argued police officers planted a knife with Mrs Gotingco's blood at his house.
He believed the two stab wounds on Mrs Gotingco's back were inflicted by police, not him, to "see if she was alive".
"What I have been convicted of is fabricated against me," he said.
Crown counsel Mark Lillico maintained Robertson had deliberately run down Mrs Gotingco.
He said the blood found in the woman's lungs was from when Robertson slit her throat.
"He didn't seek help for her [when he ran her down]," he said.
"He scouted out the cemetery before the collision."
Robertson disabled her in the way of breaking her legs and ribs, before raping her, he said.
"She was healthy and much less powerful than Robertson," Mr Lillico said.
Mr Lillico said the crash analysts concluded there were no evidence of Robertson swerving to avoid Mrs Gotingco.
There was no evidence of skid marks from tyres from his car on the road where she was hit, he said.
Robertson raped and murdered Mrs Gotingco three months after the supervision order was imposed.
Mr Lillico reminded the judges of Robertson's past offending was of assault and abduction.
Robertson was 18 when he kidnapped and molested a 5-year-old girl in Tauranga in 2005.
He is now appealing his sentence of life imprisonment with a minimum-non-parole period of 24 years.
The court reserved its decision.