In a sentence indication given in April last year, Judge McDonald accepted that Anaru was potentially entitled to a further "substantial" discount if, after pleading guilty to his offences, he was willing to give evidence against Johnstone.
A month later, Anaru admitted his offending to police and offered to become a Crown witness had Johnstone not pleaded guilty on the second day of trial before the complainant completed her evidence in chief.
The Crown said Anaru's offer of assistance was of low value because its case against Johnstone was strong.
Anaru's credibility was weak and it was the complainant's evidence that was the crucial factor in Johnstone's decision to plead, the Crown argued.
Anaru replied that even if the Crown had a strong case, his offer involved risk to himself and his family, made worse by the fact that his offer was spoken to in open court by Judge McDonald instead of it being dealt with confidentially.
The Court of Appeal agreed Anaru's offer should have been dealt with by a separate confidential memorandum and not referred to in open court.
However, the court said Anaru had not been given any assurance his offer would be kept confidential and, had he given evidence, it would have soon ceased to be.
The Court of Appeal rejected Anaru's claim he had been at risk since his offer, that he was a segregated inmate and must on his release, leave his home town. The court granted an extension of time for him to appeal but dismissed the appeal.