Court of Appeal Judgement: R v T [2010] EWCA Crim 2439

On 26th October 2010, in the Court of Appeal, Lord Justice Thomas and Mr Justices Beatson and Kitchen delivered their judgement following an appeal against the conviction of T for murder. One of the grounds for appeal was the way in which footwear evidence was presented.

As not everyone will have had the opportunity to read their Lordships’ judgement I am attempting to précis the document. I will quote the judgement as it appears; I am making no attempt to interpret their Lordships’ meaning or comment on their decision.

The Evidence

Footwear marks were recovered by an experienced footwear examiner at the crime scene and compared with shoes (trainers) from the appellant’s house.

His examination revealed

i) the type and configuration of the pattern (and hence size) of the trainers were the same as the marks at the scene. The pattern type was common.

ii) The wear on the trainers was greater than that on the shoes that made the marks. This could be due to additional use in the intervening period.

iii) Some of the marks had features which might have resulted from damage to the trainers; the trainers from the appellant showed no such damage.

There were three explanations for this

a) the marks were the result of an artefact on the floor;

b) the particular features could have worn away;

c) the marks could have been caused by a small stone which had subsequently been dislodged.

The overall conclusion was “ ..it is somewhat unlikely that the observed correspondence would have been obtained as a result of mere coincidence had the recovered footwear not made the marks in question. …..there is at this stage a moderate degree of scientific evidence to support the view that the Nike trainers recovered from the appellant had made the footwear marks.”

After the trial the scientific notes were examined by a scientist with ‘no experience whatsoever in footwear mark comparison’ who noticed that a formula and values were set out and that a Bayesian approach had been used but not explored at the trial.

This was then put before the Court of Appeal and explored.

It became clear then that there was no mention in the report of likelihood ratios, statistical information or the formula even though they were in fact used; the conclusion was solely expressed in terms of the verbal scale. Also that trial counsel was not made aware of any use of statistics.

The scientist explained that he had bases his opinion on his experience and the formula for calculating a likelihood ratio merely as a guide. He used very conservative figures to produce likelihood ratios for the frequencies of the pattern (P) and size (C) and the amount of wear (W) and damage (D) and that a database of 8,122 shoes had been used for the calculation of P. He multiplied these four values together to arrive at the LR of 100. This figure was very much more favourable to the appellant than the one which would have resulted if a figure for P was based on the population as a whole. This would have given a likelihood ratio of 26,400 or ‘very strong support’.

The Judges discussed the development of likelihood ratios in England and Wales and compared and contrasted this to the practice in The Netherlands, New Zealand, Switzerland, Australia and the USA. They pointed out that the evaluative approach is not universally adopted within the UK.

Considerations

The Judges then addressed the issue of whether a footwear examiner, having concluded that a mark could have been made by a defendant’s shoe, could express an evaluative opinion on the probability that it was.

Their Lordships accepted that where a sufficiently reliable database was available, as in the case of DNA, then a straight statistical model could properly be used. However as this was not the case with footwear the examiner could not attempt to use a formula to calculate probabilities. Furthermore the data used in this case is only available to examiners from one organisation.

However they acknowledge that there might be times when an examiner could go further to express a more evaluative opinion where the conclusion is that the mark “could have been made” by the footwear but that no likelihood ratio or other mathematical formula should be used in reaching that judgement. Where this is the case it should be made clear that the view is based on experience and the word “scientific” should not be used.

They recommend that where an evaluative opinion is expressed factors that enable this, including data, must be clearly set out so that the report can be considered at a pre-trial hearing.

Conclusion

On the basis that i) the statistical evidence was inherently unreliable, ii) the jury had not been told the basis on which the conclusion had been reached and iii) the process had not been transparent, the conviction was unsafe. Their Lordships had no criticism of the scientist who they agreed was following standard procedures.

However, they concluded:

“For the future strict compliance with the requirements of transparency (as discussed above- my comment) should ensure that in each case where an expert provider of a forensic opinion seeks to develop a new way of arriving at an opinion, that new way can be examined in open court applying the ordinary principles for the admissibility of expert evidence.

We think there is no need for any new process”

The appeal was allowed and the conviction quashed.

Throughout the judgement the Judges referred to papers (among others referring to overseas) as follows:

  • “A Bayesian approach to interpreting footwear marks on forensic casework” by Evett, Lambert and Buckleton
  • “Principles of Interpretation- application of the likelihood ratio in marks cases” by Jackson, Champod and Evett
  • “Standards for the formulation of evaluative forensic science opinion” as discussed by the Forensic Science Advisory Council in December 2008.

Also to

  • Professor Ormerod on Adams [1996] Crim L R 898
  • Professor Glanville Williams “The Mathematics of Proof” [1979] Crim L R 346-350
  • Professor Redmayne “Doubts and Burdens: DNA Evidence, probability and the Courts” [1995] Crim L R 464
  • Chapter 4 of “Expert Evidence and Criminal Justice, Phipson on Evidence, 17th ed. (2010) para 34-36 to34-38.
  • Roberts and Zuckerman’s Criminal Evidence p. 123-132.

They refer to cases of Adams, Reed and Reed, Weller, Henderson, Pendleton, Doheny, Dennis Adams and George.

Full details of all these references can be found in the Judgement.

Additional evidence from the Forensic Science Regulator and two other scientists, expert in footwear marks and case assessment and interpretation was also considered by their Lordships.

Dr Ann Priston

President, Forensic Science Society