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The Evidence that Never Was 1 - Evidence in Need of Evaluation

April 01 2017

In her report published in January 2017 Dr Tully, the Forensic Regulator, warned that cuts to forensic science budgets are compromising quality and now pose a risk to justice. We agree. Cuts have been made through investigating less, by submitting fewer samples for examination and by cutting out experienced evaluation. Unfortunately we regularly see the consequences of this in our work.

For example: we were recently instructed to review the footwear mark evidence in a burglary case, where it was reported that two partial footwear marks had been recovered from a worktop inside the point of entry. The Crown expert had concluded that the defendant’s right shoe corresponded to both marks in terms of pattern and apparent size and could have made both of them. The case proceeded to trial. Our expert agreed that one of the marks corresponded to the heel of the shoe in the manner described, however, this in itself was not probative and our expert had concerns over the sizing and general wear of the second mark. During his examination he noticed annotations on the lifts, which he recognised as being typical of those used by CSIs to indicate how 2 lifts abut. When the CSI's statement was retrieved it became clear that the lifts actually recorded a single mark. Once reconstructed and examined as a single mark there was a significant size discrepancy. The Crown expert agreed and the charge was dropped because the defendant's shoes were too large to have been responsible for leaving the mark.

Typically, inexperienced evaluation manifests its biggest risk in trace evidence cases where secondary transfer of small fragments of case-relevant evidence is misinterpreted or ascribed evidential weight it cannot bear.

Case example: three men were arrested shortly after a dwelling house burglary in which a window was broken. The third man had two glass fragments in his hair matching the broken window. At trial, the Crown scientist opined that it was highly unlikely that this resulted from secondary transfer because the other two men also had low numbers of glass fragments on them. Our experience of secondary transfer led us to look at this more closely. Analysis of the SOCO and police statements confirmed that not only was there opportunity for secondary transfer by association shortly after the event, but also that a police officer who had contact with the defendant could equally have been the vector of transfer for such a low number of particles. Finally, we pointed out that eye witness accounts described two men running from the scene, not three. The Crown expert changed her mind and agreed our findings. The third man was acquitted.

In a more serious, but not uncommon, scenario, one defendant claimed to be a bystander to an assault which proved fatal. Low numbers of fibres from the victim's jumper were found on the jersey of this defendant. The Crown scientist presented evidence that this provided moderate support that the two had been in direct contact. On examination of the clothing, our expert found that the defendant's jersey shed its fibres very readily but that none of these were found on the victim's jumper; in which case the simplest evaluation might consider why, if the two had been in direct contact, were none of the defendant's jersey fibres found on the victim?  The most likely explanation: indirect transfer. At court the Crown scientist had to concede this was a possibility.

These are three simple examples which highlight the damage cost cutting in the form of incomplete or inexperienced evaluation is doing to our Criminal Justice System. Of concern to all should be that the Crown scientists in these cases all work for fully accredited Forensic Service Providers, hence the importance of the Defence obtaining their own interpretation and evaluation.


Guy Cooper

Dr Guy Cooper
BSc(Hons), PhD

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