The thoughts of Kerri Allen from

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The absence of evidence does not necessarily indicate the absence of something, and while this may be true in many instances – for example, if a person’s clothing did not have blood on it due to the fact that they didn’t commit the crime or because the victim was not bleeding sufficiently for blood to be transferred – there will be times when more consideration is required before reaching a neutral conclusion.

Absence of DNA profiling evidence

DNA is the ‘gold’ standard in biological evidence, and failure to obtain a DNA profile often indicates that there is no scientific evidence to back up either the prosecution or defense case. When body fluids are discovered, however, the presence of these alone may provide evidentiary value.

Considering the body fluid findings and alternative scenarios

Sexual assault cases are often complicated, but differences in the level of detail in each party’s narrative of events might provide avenues for scientific study. Consider a recent example, in which both parties agreed that sexual intercourse had occurred, yet there was disagreement over whether or not oral sex had taken place – the defendant claimed it had, but the accuser denied this. DNA analysis has failed to identify the source of trace amounts of semen found in mouth swabs taken shortly after events. The prosecution’s specialist said that the scientific evidence did not aid in determining which version of events was true, however we reached a different conclusion.

The Devil’s in the detail

The presence of semen on mouth swabs suggested relatively recent introduction of semen into the complainant’s oral cavity, something that could be explained through the oral intercourse the defendant claimed. Within the framework of the allegations made by the complainant, there would be effectively no opportunity for semen to have been deposited into her mouth, but additional information provided included mention of possible oral intercourse with a boyfriend 3 days prior to the alleged incident. Whilst published data is limited, studies show that, in most cases, semen is lost from the mouth in less than 24 hours; the maximum recorded is 49 hours. Notwithstanding this, the prosecution’s scientist concluded that the findings would be equally likely if oral intercourse had been 3 days or a matter of hours before the mouth swabs were taken. Our assessment, based on the scientific research, was that persistence of semen in the mouth 3 days after oral intercourse would be extremely unlikely, and therefore that the findings provide support, albeit limited, for the defendant’s version of events.

Thinking beyond neutral conclusions

Beware of neutral conclusions, particularly when DNA profiling has failed but body fluids have been detected. Next time you read ‘in my opinion the findings do not assist’ be sure to get this checked.

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