Can Biological Evidence Be Challenged?

Why Good Forensic Science Should Always Withstand Scrutiny

DNA evidence, blood pattern analysis and body fluid evidence can play a significant role in criminal proceedings. Understanding when these findings should be challenged helps criminal defence solicitors, barristers and other legal professionals evaluate forensic evidence and ensure it is presented fairly, accurately and in the context of the wider case. 

Forensic biology can provide valuable scientific findings in criminal proceedings. DNA recovered from beneath a deceased’s fingernails, blood patterns at a scene or the presence of a body fluid can all appear to provide clear and definitive answers about what happened. 

However, these findings cannot always establish how biological material came to be present, when it was deposited or whether its presence supports one account of events over another. Those questions require the science to be considered alongside the wider facts of the case. 

Biological Evidence Is Compelling, but It Is Not Beyond Challenge 

Challenging biological evidence is not about questioning accredited laboratory processes or undermining robust scientific methods. It is about ensuring that scientific conclusions are supported by the available evidence, that any limitations have been recognised and the possibility of another reasonable explanation has been considered. 

For criminal defence solicitors and barristers, recognising when biological evidence should be challenged is an important part of preparing a case. Independent forensic review can identify additional avenues of enquiry, highlight scientific limitations or provide alternative explanations that assist the court in reaching balanced, evidence-based decisions. 

Ultimately, the purpose of independent review is not to create doubt where none exists. It is to ensure that biological evidence is presented fairly, accurately and with the scientific context needed to support the administration of justice.

Biological Evidence Is Powerful, but It Is Rarely the Whole Story

Biological evidence should never be considered in isolation.

A DNA profile may identify the individual from whom biological material may have originated, but it cannot necessarily determine exactly when that DNA was deposited or whether it resulted from direct contact, indirect transfer or everyday activity. Blood pattern analysis may assist in reconstructing events, but its value depends upon careful evaluation of the scene, the available evidence and the specific accounts of those involved. Similarly, the presence of a particular body fluid may be highly significant, but its evidential value depends on how and when it may have been deposited, how it relates to the wider circumstances of the case and again, the specific accounts of those involved.

Criminal defence solicitors and barristers should therefore look beyond the laboratory result. The significance of biological evidence depends on the questions being asked, the information available to the expert and whether other scientifically plausible explanations have been considered.

When Should Biological Evidence Be Challenged?

Legal professionals do not need to become forensic scientists to identify when biological evidence may require further scrutiny. However, they do need to consider whether the original expert had sufficient relevant case information to address the issues in dispute.

Before any examination begins, forensic biology experts develop a scientific strategy designed to answer specific questions. Where competing accounts of events are available, those accounts help determine those questions and which examinations are likely to provide meaningful evidence. Scientists must also consider the order in which examinations are carried out to ensure that one test does not unnecessarily compromise future opportunities for examination.

New information may emerge as an investigation progresses. Witness statements, disclosure material or instructions from the defendant may provide context that was not available when the original forensic examinations were undertaken. At that stage, the forensic evidence should be reevaluated in light of this new information.

A robust case review should include, as well as reviewing the accuracy of the scientific findings, a consideration of whether the most appropriate items were examined and tests utilised, and often most crucially, what the findings mean within the context of the case and specifically in relation to the accounts put forward by the prosecution and the defence.  For example, our forensic scientists may review whether DNA transfer or persistence has been fully explored, whether the limitations of blood pattern analysis have been recognised and whether further biological examination could assist.

Questions Every Criminal Defence Solicitor and Barrister Should Ask

Forensic biology evidence can be highly persuasive, but its significance may be overstated if its limitations are not fully understood. The question is not only whether the laboratory testing was carried out correctly, but also whether the conclusions are supported by the findings and whether further review could assist the court.

Questions worth considering include:

• Were the most appropriate items examined and tests utilised?
• Was all relevant case information and alternative accounts available when the original scientific opinion was formed?
• Could indirect DNA transfer, DNA persistence or innocent contact provide an alternative explanation for the findings?
• Have the limitations of the blood pattern analysis been fully explored?
• Could additional DNA profiling or body fluid examination provide further information?
• Do the scientific conclusions accurately reflect the evidence, or do they go beyond what the scientific findings alone can support?

These questions are intended to ensure that biological evidence has been evaluated thoroughly and that expert conclusions are presented to the court fairly, proportionately and with an appropriate understanding of their limitations and their context within the wider case.

Case Study: When Additional Context Changed the Significance of DNA Evidence

A murder case reviewed by Forensic Access scientists demonstrates why biological evidence should always be considered within the wider context of a case, and why independent expert review can be so valuable in criminal proceedings.

The defendant was charged with murder after DNA that could have come from him was recovered from beneath the deceased’s fingernails. This was reported by the original scientist as supporting the prosecution’s case that an altercation had taken place on the day of the man’s death rather than the defendant’s case that the two fought three days prior. Forensic Access was instructed to conduct an independent defence review. The DNA profiling and resultant match was checked and agreed.  The next step was to consider the evidence in the context of the case and in relation to the alternative accounts put forward by prosecution and defence.

Scientific research studies to date largely found that DNA did not persist at detectable levels more than two days after deposition.  It was on this basis that the original scientist had reached their conclusions.  However, on review it appeared that the wider context of this particular case did not appear to have been take into consideration.

The deceased lived an itinerant lifestyle in which he did not regularly wash or change his clothes. Postmortem images showed that the deceased had long and very dirty fingernails.  Therefore, the findings of studies based on laboratory staff volunteers would not necessarily apply to this case.

The findings were revaluated in light of this additional case context and the original scientist agreed with the Forensic Access scientist that it was not possible to determine whether the DNA was deposited at the time of the murder or three days prior to this.  The findings did not assist in differentiating between the prosecution and defence accounts and should be treated as neutral.

The laboratory findings themselves had not changed. The DNA profile remained the same. What changed was the context in which that evidence needed to be evaluated.

Independent Forensic Review Strengthens the Administration of Justice

Although independent forensic review is often associated with criminal defence, its purpose is much broader than supporting one side of a case. The role of an independent forensic expert is to assist the court by providing objective scientific opinion, evaluating the available evidence and ensuring that any conclusions are fully supported by the evidence.

An independent forensic biology review may identify further avenues of enquiry, explain scientific limitations or provide reassurance that the original conclusions are robust and well supported. Where it confirms that the conclusions reached by the prosecution are scientifically sound, it still provides value by giving legal teams confidence that the biological evidence has been independently assessed before it is presented in court.

Experienced forensic biologists recognise the limits of the available evidence and that not every scientific question has a definitive answer. Recognising and clearly stating these limitations is as important as understanding the strengths of the evidence and is an essential part of objective forensic science.

Ensuring the Court Has the Full Scientific Picture

Good forensic science should never be afraid of scrutiny. On the contrary, robust scientific evidence should be capable of withstanding challenge, because challenge encourages careful evaluation, proportionate conclusions and balanced expert opinion.

Further Learning Through Training and Webinars

Challenging biological evidence begins with understanding it. Alongside casework review and re-examination, Forensic Access delivers training and webinars on a range of forensic biology topics, including DNA evidence, blood pattern analysis and body fluid examination. These sessions help legal professionals understand what scientific findings can demonstrate, but also their limitations and potential evidential significance.

By improving understanding at an early stage, legal teams are better equipped to ask informed questions, instruct appropriate experts and identify the issues that may require further scrutiny as an investigation progresses.

Do You Require Forensic Biology Expert Support?

At Forensic Access, our forensic biology scientists have extensive experience reviewing cases for both prosecution and defence, advising the legal team and presenting expert evidence in court. By combining scientific expertise with an objective, evidence-led approach, we help legal professionals understand what the biological evidence means, its limitations and how those findings assist in evaluating the issues before the court within the context of that case.

If you require expert support in cases involving DNA evidence, body fluids, blood pattern analysis or a wider range of forensic evidence, get in touch with our casework team on 01235 774870 or at science@forensic-access.co.uk.