C, R. v

Low-template DNA evidence is not inadmissible solely because the amount of DNA falls below a stochastic threshold. The question under Police and Criminal Evidence Act 1984 is whether the profile is reliable, having regard to stochastic effects and reproducibility. If it is admissible, its weight is for the jury.

A preparatory hearing under Criminal Procedure and Investigations Act 1996 is exceptional. It cannot be used merely to obtain an interlocutory appeal on a fact-sensitive scientific ruling, and it cannot be declared retrospectively after the ruling has been made.

The appellant was to be tried for a historic rape. Later DNA analysis of vaginal swabs produced a mixed profile. The Crown contended that the minor profile matched the appellant. The defence challenged the reliability of the SGM+ and LCN DNA evidence and sought its exclusion under section 78 of the Police and Criminal Evidence Act 1984.

Following a voir dire, the trial judge admitted the evidence. After giving that ruling, he declared the hearing to have been a preparatory hearing under section 29 of the Criminal Procedure and Investigations Act 1996 and granted leave to appeal. The appeal concerned the admissibility ruling, the validity of that order, and the proper procedure for such challenges.

1. The court quashed the preparatory-hearing order. The trial judge had correctly admitted the DNA evidence, but the case did not satisfy the statutory conditions for a preparatory hearing. The Court of Appeal therefore had no jurisdiction to entertain an interlocutory appeal founded on that invalid order.

2. The decisive question under section 78 of the Police and Criminal Evidence Act 1984 was the reliability of the profile, not whether the minor contributor's DNA was below 100–200 picograms. The stochastic threshold in Reed & Reed [2009] EWCA Crim 2698 concerned the total DNA subjected to analysis. A profile derived from less than 200 picograms may be reliable if stochastic effects are properly addressed, including by reproducible results from repeated runs. The judge was entitled to accept the uncontradicted Crown expert evidence that the results were sufficiently reliable. Their weight was for the jury.

3. Section 29 of the Criminal Procedure and Investigations Act 1996 requires likely substantial benefits arising from a hearing because of the case's complexity, seriousness or likely length. Complex DNA evidence could be presented intelligibly to the jury through firm case management or, if necessary, an ordinary voir dire. The wish to obtain an interlocutory appeal did not justify a preparatory hearing. The court applied the caution in I, P, O, I & G [2009] EWCA Crim 1793: such appeals are confined to rare, discrete legal issues capable of authoritative resolution without evidence.

4. Section 29 authorises an order that a preparatory hearing shall take place. It does not permit a judge, after deciding the relevant issue, to declare retrospectively that a preparatory hearing has already taken place. If the statutory criteria emerge during a pre-trial hearing, an order may then be made before the relevant ruling.

5. Challenges to DNA evidence should comply strictly with Part 33 of the Criminal Procedure Rules 2010. A defence expert must provide a signed, verified statement identifying the alleged methodological or analytical defects and why they fundamentally undermine reliability. Experts should identify their agreements and disagreements. Any section 78 hearing should be tightly managed, confined to defined issues, and not used for advance cross-examination of trial experts.

• Court of Appeal (Criminal Division): Quashed the retrospective preparatory-hearing order and held that the statutory conditions for such an order were absent. It upheld, in its observations, the trial judge's approach to the admissibility of the DNA evidence.
• Crown Court: The trial judge admitted the DNA evidence after a voir dire under section 78 of the Police and Criminal Evidence Act 1984. He subsequently declared the hearing a preparatory hearing and granted leave to appeal. No lower-court citation was stated.