The Parole Board says there is no alternative but to keep a paedophile advanced dementia in prison.
Donald Liddington, 76, is serving a sentence of preventive detention imposed in 1998 for a series of sexual offences against young girls, including the rape of a preschooler.
The board said Liddington has advanced dementia and has no understanding of his situation.
It said someone has come forward to be his welfare guardian but they have not yet been formally appointed.
In the meantime, the board said the best place Liddington can be kept is the high-dependency unit at Rimutaka prison.