"A brief encounter; a date, with death its conclusion. A young woman, Grace Millane, died; a young man, the appellant, is now serving a life sentence for her murder. He accepts his actions caused her death. But he says he is not culpable of her murder."

This haunting description was how the Court of Appeal started its 63-page judgment, which today dismissed an effort by the British backpacker's murderer to quash his conviction 17-year non-parole period.

The court also described the killer's actions after Millane's death as "indicative of a degree of wholly self-regarding wickedness".

Millane, who had been travelling the world, went missing on the eve of her 22nd birthday after matching with her killer on the dating app Tinder in December 2018. The pair met near a Christmas tree under Auckland's Sky Tower and spent the night drinking at nearby bars.

She was last seen alive on CCTV with the man, walking towards his downtown Auckland apartment.

The killer controversially argued at trial that Millane died due to complications from consensual sex while both were highly intoxicated and engaged in BDSM.

Despite losing today's appeal, the murderer continues to claim his innocence and has already launched a second challenge to New Zealand's Supreme Court. The top court also made a last-minute order today continuing the man's name suppression.

At the Court of Appeal in September, the killer's lawyer, Rachael Reed QC, argued trial judge Justice Simon Moore should have told the jury the prosecutors had to disprove consent - or an honest belief in it - to obtain a conviction.

Other conviction appeal grounds related to the admission of probability evidence and the judge's directions on expert and propensity evidence.

However, the Court of Appeal's bench, which consisted of Justice Stephen Kos, Justice Patricia Courtney and Justice Mark Cooper, ruled the Crown was not required to disprove consent or an honest belief in it.

"On appeal at least, the Crown does not suggest he set out to kill Ms Millane. Rather, it says he intended to cause her bodily injury by strangulation, for sexual effect, knew that was likely to cause death and consciously ran that risk," the judgment reads.

"Consent is not available as a matter of law where there is an intent to cause injury known to be likely to cause death, that risk is run, and death ensues."

The court also found no credible narrative of consent, or honest belief in consent, established on the evidence.

And it found Justice Moore's summation to the jury was appropriate regarding the propensity evidence.

"This concerned the evidence of three witnesses who gave evidence as to the appellant's interest and/or experience with erotic asphyxiation during sexual intercourse," the decision reads.

"Two had sexual intercourse with the appellant in the weeks before he met Ms Millane. One of these, Ms J, had been terrified by the appellant's suffocation of her and thought she was going to die. A second, Ms M, had the opposite experience and considered the appellant behaved appropriately in restricting her breath, by consent, to enhance her pleasure."

The Court of Appeal said it did not consider Justice Moore was required to give what is known as a "negative propensity direction" in respect of M's evidence, or a failure to do so gave rise to a risk of a miscarriage of justice.

"The jury would have had no difficulty weighing that evidence and, as we note, each party gained support from it: the Crown, in that the appellant was an experienced practitioner of erotic asphyxiation; the defence, in that he behaved entirely appropriately with Ms M."

The Court of Appeal also found the judge's summing-up directed the jury appropriately on the pathology evidence, which included three expert witnesses.

"Four potential mechanisms resulting in death were canvassed and the force and time required to effect each were explained and then tested in cross-examination.

"The summing-up provided a clear summary of the competing expert opinions on cause and time without offering detailed evaluation, analysis or endorsement, given no issue as to admissibility of the competing views had arisen."

Evidence of a short study of death arising from erotic asphyxiation in Poland was also explained to the jury.

"We consider the study neither reliable nor relevant to a fact in issue," the Court of Appeal said.

"It ought not to have been put before the jury or have been used in cross-examination of the expert witnesses. No objection was taken to its introduction or use at trial. It would have been preferable if a clear direction had been given that it could not be used to deduce guilt on the basis of probabilistic reasoning."

However, the appeal court said its admission and the absence of such a direction did not give rise to a material risk of a miscarriage of justice.

"The proposition that death resulting from erotic asphyxiation is very rare was an accepted fact. The jury was not invited to use statistical probability reasoning to reach a finding of guilt, and it was extremely unlikely in context that the jury would have done so."

When considering the killer's sentence, the Court of Appeal ruled Justice Moore was correct when imposing a non-parole period of 17 years.

"Ms Millane was particularly vulnerable, being intoxicated, in a strange apartment, naked, in the arms of a comparative stranger with whom she thought she had 'clicked' (and could
therefore trust), and with his hands about her throat," the decision reads.

"The judge was correct in finding the murder of Ms Millane was committed with a high degree of callousness."

The Court of Appeal said the killer's attitude to the likely struggles of Millane, and certain lapse into unconsciousness, displayed a disregard for her.

"To be plain about matters, it really is very difficult to imagine much greater vulnerability than the situation Ms Millane found herself in on the evening of Saturday, December 1, 2018," the judges said.

At about the time of Millane's death, her killer also took a shower, failed to call 111, searched the internet for methods of body disposal, looked at pornography online, and took intimate photos of Millane's naked body.

He also began taking steps to dispose of her body, which was discovered in a shallow grave in Auckland's Waitākere Ranges, and went on another date while Millane's body remained in his CityLife hotel apartment.

"We conclude that this behaviour is indicative of a degree of wholly self-regarding wickedness throughout the incident and its aftermath.

In a statement provided to the Herald, Millane's family thanked the judges and others involved with the case.

"We would also like to thank the people of New Zealand for the love and support they have shown to Grace and our family over the last two years.

"She was enjoying the first of what would have been a lifetime of adventures before her life was so cruelly and brutally cut short by her murderer."