The majority in Morgan v R  NZSC 23 (16 March 2010) do not explain why they reach the opposite conclusion to that of the dissenting Chief Justice. All Justices agreed that the issue came down to whether there was unfairness in admitting the contested evidence. The Chief Justice explained in detail why she thought there was unfairness. In the absence of a detailed response by the majority we are left feeling some disquiet about the soundness of the majority's conclusion.
Here the contested evidence was a statement previously made by a witness who was now hostile to the extent that he claimed not to remember the events in issue, and the making of any previous statement about them.
In contrast to the earlier position, under the Evidence Act 2006[NZ], any statement that is admissible is admissible to prove the truth of what it asserts. Where a witness is declared hostile, a relevant previous statement by that witness can become admissible. It may be elicited in cross-examination by the party that called the witness: s 94, or the Judge may permit such cross-examination even if the witness is not hostile: s 89. If the witness is hostile to the extent of refusing to be cross-examined, it is arguable that he is not a "witness" within the definition of that term, and his prior statement is hearsay. But even if it is not hearsay, fairness should require reasonable assurance that the statement is reliable when the s 8 discretion to exclude it is being considered.
The matter comes down to this (as expressed in the majority judgment):
The majority held that difficulties that might have arisen if defence counsel had attempted to cross-examine the witness on the prior statement were not such as to give rise to unfairness. No elaboration of that was offered. So we don't know why it was fair to admit the statement. The Chief Justice explained her conclusion by pointing out that in this case there was no other evidence sufficient to provide a reasonable assurance that the prior statement was reliable. The majority alluded to "a number of circumstantial features pointing to Mr Morgan's involvement, established elsewhere in the Crown's evidence" (para 45).
Still, the case is authority for, or illustrates, the following points: statements are admissible for their truth; admissibility is subject to s 8; there is a need for particular care to avoid unfairness when there can be no cross-examination of a hostile witness; the judge should hear evidence in voir dire before ruling on admissibility and should include an exploration of the witness's willingness to be cross-examined.
A significant omission from the factual narrative is whether the witness, a cell-mate of the accused, knew what the accused was charged with at the time he reported to the police that the accused had confessed. The Court of Appeal judgment summarises the facts ( NZCA 537):
" Mr Roskam shared a cell with the appellant shortly after the appellant was remanded in custody. Mr Roskam said in a statement to the police that he and the appellant had been watching a programme called “Police 10-7” which featured the robbery at issue in the present case. The appellant became very excited, and subsequently (some days later) told Mr Roskam that he had committed the robbery."
In the absence of this important fact, I will assume that the cell-mate knew, at the time he reported the confession, what the accused was charged with.