He and David Reynolds, 41, are now both in prison for what happened after they took her to a motel unit.
The Napier District Court was told on Monday that the woman has a diagnosed condition which causes cognitive impairment and communication difficulties.
She did not know the men when they took her to the motel, where a number of sexual acts involving both men took place.
Reynolds previously pleaded guilty to violating the woman and was sentenced in September last year to four years and five months in prison.
Rigby faced five charges for which he was the alleged principal offender.
He elected trial by jury, who found him guilty on one count - of sexual violation by rape - and not guilty on the others.
Judge Russell Collins said the victim was vulnerable because of her diagnosed condition and because she had been drinking, although to what extent was unclear.
Evidence of her intoxication level was uncertain and contradictory.
Rigby may have had grounds to believe the woman was consenting early in the encounter.
However, Crown Solicitor Steve Manning said that when it came to the final act, she was crying and there was evidence she had said no.
Judge Collins said Rigby’s actions towards the woman were “callous and uncaring, and were selfish”.
In relation to the charge for which he was found guilty “they crossed the line and became criminal”, he said.
After hearing submissions from Manning and defence counsel Shane Robinson, Judge Collins set the starting point for Rigby’s sentence at six years in prison.
He said he was unable to make any deduction for previous good conduct because Rigby had convictions for violence and drink-driving.
He was also unable to make deductions for a guilty plea, as Rigby had chosen to go to trial, nor for remorse, as there was none.
“You take the position that no offending occurred. You continue to protest your innocence,” Judge Collins said.
He gave Rigby a nine-month discount for more than two years spent on restricted or electronic bail.
Rigby was sent to jail for five years and three months.
Ric Stevens spent many years working for the former New Zealand Press Association news agency, including as a political reporter at Parliament, before holding senior positions at various daily newspapers. He joined NZME’s Open Justice team in 2022 and is based in Hawke’s Bay. His writing in the crime and justice sphere is informed by four years of front-line experience as a probation officer.
