Akshay Chand, 19, was found not guilty of murdering Christie by reason of insanity in the High Court at Auckland yesterday.
He had earlier admitted kidnapping Christie and putting her through a terrifying knifepoint ordeal last September.
Justice Helen Winkelmann sentenced Chand to three years in custody on those charges.
She took into account Chand's age, mental health and previous "good character". But she also spoke of the horror he put Christie and her family through.
He will serve that time at the Mason Clinic where he is being detained indefinitely as a special patient.
Psychiatric experts deemed him insane when he killed Christie and said he suffered from a schizophrenic mental illness.
A voice in his head "compelled" him to stab her.
- Anna Leask of the New Zealand Herald
