The successful use of the defence has raised eyebrows this week but two of New Zealand's leading psychiatric experts have no doubt that Chand was insane when he killed Christie - and had been suffering an untreated schizophrenic episode for up to 18 months.
They both say there is no way he could have faked his symptoms. They say he has a serious mental illness with a very poor prognosis and recommended he be detained as a psychiatric patient indefinitely.
Under the Crimes Act 1961, no one can be convicted of an offence if they are proven to have a "disease of the mind" to such an extent that they do not understand the nature of the act, or know that the act was morally wrong.
Chand's lawyer, Mary-Anne Lowe, arranged for Dr David Chaplow to assess whether a mental illness was present.
Dr Chaplow was given access to Chand's court file, including interview transcripts and medical reports. He interviewed Chand twice at length before framing his final decision.
Chand told Dr Chaplow he started hearing a voice in his head in January 2011. It was a female with a soft English accent and it had a strong control over Chand.
He later recognised her voice as that of Pauline, a young girl he had attended school with in Wales.
Chand told Dr Chaplow that Pauline wanted him to kill Christie. He felt compelled to act on what Pauline told him.
Dr Chaplow concluded Chand was paranoid, delusional, lacked insight, suffered hallucinations and was depressed - all symptoms of a schizophrenia-like illness.
Dr Chaplow's report was given to the Crown, who asked Professor Ian Mellsop to assess Chand.
Dr Mellsop told the court he was sceptical of Chand's insanity at first, but soon came to the same conclusion as Dr Chaplow.
