A man and two women jailed for murdering a 65-year-old man who was left for dead in a Christchurch car park have had their appeals against conviction rejected.

Cyle Robert Jetson, Debra Jean Tihema and her daughter Mylesha Port Tihema were found guilty of murdering Pierclaudio Raviola following the brutal attack in March 2017.

Raviola, a bus driver and chef, was attacked when he showed up at a Bromley house on the night of March 23.

He was bundled, unconscious, into the boot of a car and dumped at the Sumner Surf Lifesaving Club with serious head injuries.

A teenage co-offender then used Raviola's keys to burgle his Phillipstown home.

Raviola was found the next morning. He was rushed to hospital in critical condition with a fractured skill and swollen brain but died two days later.

Jetson, Debra Tihema and Mylesha Tihema received sentences of life imprisonment with non parole periods of 11, 17 and 10 years respectively.

At a Court of Appeal hearing in Wellington earlier this year, the trio appealed their convictions, with Mylesha Tihema's lawyer saying she was "effectively a bystander to the trial" due to her mental disabilities.

Lawyer Nick Chisnall asked the appeal court to retrospectively assess whether his client was fit to stand trial at the time.

Tihema has Foetal Alcohol Spectrum Disorder, complex PTSD, and Disruptive Mood Dysregulation Disorder.

He noted Tihema was absent at multiple points of the trial, including when the defence case opened.

But the appeal judges were unconvinced Tihema didn't understand what was happening at trial, saying an affidavit from her to that end was for the most part "demonstrably incorrect".

They said it appeared to be a case of "strategic lying" and that "Mylesha knows that
to say she didn't understand anything will be good for her chances of success on appeal".

They found though some of her instructions to her lawyers at trial were inconsistent, it wasn't compelling evidence she was unfit to stand trial.

"The fitness test does not require a defendant to always act wisely in their own best interests," they said.

Jetson's lawyer, James Carruthers, said parts of his interview with police shouldn't have been used due to the overly persistent interview method used.

He referred to officers making it clear they thought Jetson was lying and unfavourably comparing his account to that of his co-offenders, as well as telling him the co-offenders had blamed him for the crime.

"The admissions came after a couple of hours and only made after these transgressions."

But the appeal judges said the officers treated Jetson with "courtesy", but noted the interview technique was not ideal.

"We are not persuaded the persistence was oppressive or intimidatory in nature. It did not place unfair pressure on Mr Jetson and it did not in fact overbear or influence him."

They did find a "causal nexus" between what the officers said and Jetson's admissions, and said there were grounds to find the evidence was "improperly obtained".

But the exclusion of the evidence would be a disproportionate response to any impropriety.

Debra Tihema also appealed, with her lawyer, Nick Rout, saying the defence should have been able to call evidence showing Mylesha Tihema had a propensity for violence.

He said the forensic evidence showed the senior Tihema's blows with the shotgun stock would not have been enough to kill Raviola.

But the appeal judges said the propensity evidence would actually have weakened her case.

"The uncontested evidence was that far from withdrawing from the enterprise when a weapon was introduced, it was Debra who introduced the weapon, no one else."

The judges dismissed all the appeals.

The offending

Raviola met the Tihemas at a motel and struck up a relationship with Debra Tihema with a desire for adult company and physical affection, Justice Rachel Dunningham said in her sentencing notes.

"It is clear these feelings were not reciprocated by you. However, you quickly came to view
Mr Raviola as a source of benefits, such as money and food, and even a cell phone. You took advantage of his loneliness and good nature and you offered him physical affection in return for those benefits."

Tihema told others over text she was using Raviola for all she could get, and that she would eventually "bleed him dry".

When a gang-affiliated family member started pressuring Tihema to pay a debt, she hatched a plan to take Raviola's car from him using standover tactics.

She lured him into her home and bedroom then had her nephew, daughter and daughter's boyfriend join in assaulting Raviola.

The violent attack included Tihema hitting Raviola over the head repeatedly with a shotgun stock.

The group taped Raviola's hands together and carried him, unconscious, to the car. Another person and Jetson took the victim to the car park while the Tihemas stayed behind to start cleaning the scene.