How Is Forensic Evidence Presented in Criminal Trials?

Forensic evidence - scientific material such as DNA, fingerprints, toxicology results and digital data - can be among the most powerful evidence in a criminal trial. In England and Wales, the use of forensic science is governed by strict legal and procedural safeguards that ensure evidence is reliable, relevant and fairly presented to the judge or jury. This guide explains how forensic evidence enters a criminal trial, how it must be prepared and presented, and how both prosecution and defence work with forensic experts so that the court can properly assess scientific findings.

The Role of Forensic Evidence in Criminal Justice

Forensic evidence is used to connect a suspect to a crime scene, identify victims, reconstruct events and explain technical matters beyond the understanding of laypersons. It may be decisive in proving guilt or establishing innocence. However, scientific evidence can also be complex, technical, and potentially misleading if presented without proper context. To address these risks, courts only admit forensic evidence that is relevant, reliable and lawfully obtained, and experts giving such evidence must meet professional and procedural standards.

Gathering and Preparing Forensic Evidence

Secure Collection and Chain of Custody

Before evidence can be presented in court it must be collected, preserved and documented according to recognised scientific and legal standards. This includes:

• Recording where and how evidence was found;
• Ensuring a clear chain of custody showing who handled the material at each stage;
• Preventing contamination or degradation of samples;
• Keeping detailed laboratory records of analysis steps.

If these safeguards are not followed, the evidence may be challenged as unreliable or excluded by the court.

Forensic Science Regulator Standards

Since 2 October 2023, forensic science activities are regulated under the Forensic Science Regulator Act 2021 and an accompanying Code of Practice, which set quality and competence requirements for laboratory work and expert reports. Accredited procedures and compliance with the Code enhance the credibility of forensic evidence, although non‑compliance does not automatically render evidence inadmissible - the court will decide reliability on a case‑by‑case basis.

Expert Witnesses and Reports

Forensic evidence is typically presented through expert witnesses - scientists or specialists with recognised training and experience in a relevant discipline. An expert's role is to explain scientific findings in a way that is understandable to the court and relevant to the legal issues in the case.

Expert Reports

Before trial, forensic experts prepare written reports setting out:

• Their qualifications and the material they examined;
• The scientific methods used;
• The conclusions they have reached and the basis for those conclusions.

Under the Criminal Procedure Rules (Part 19) and Criminal Practice Directions 2023, experts must also disclose whether the forensic activity falls under the Regulator's Code and whether they complied with applicable standards.

Reports must be served on the court and the opposing party in advance to allow proper scrutiny, challenge and preparation. This disclosure obligation helps avoid surprises at trial and supports the defendant's right to a fair hearing.

Admissibility of Forensic Evidence

Forensic evidence must be relevant to an issue in the case and reliable in method and application to be admitted. The court applies established legal principles when deciding admissibility:

• Relevance: evidence must logically bear on a fact in issue;
• Reliability: the scientific methods and applications must be sufficiently sound and understood;
• Necessity: the evidence must address matters outside the ordinary experience of a judge or jury.

When dealing with novel or infrequently used techniques - such as advanced biometric analysis or emerging digital methods - judges may require additional assurance about the scientific basis before admitting the evidence.

Presentation in Court

Once admitted, forensic evidence is usually introduced through the expert witness giving oral testimony under oath. This includes:

• Examination‑in‑chief: The party calling the expert (prosecution or defence) asks questions to explain the report and findings;
• Cross‑examination: The opposing side can challenge the expert's methods, conclusions, assumptions, or any limitations;
• Re‑examination: A brief opportunity for clarification on points raised during cross‑examination.

Experts must communicate their evidence in clear language, often using visual aids such as diagrams, photographs or models to help jurors and judges understand technical material.

In some cases, particularly when the science is agreed by both sides, the court may accept summaries or joint statements without requiring extensive oral testimony - but this requires agreement or a specific court direction.

Special Forensic Procedures: Streamlined Forensic Reporting

In many cases, forensic evidence is introduced through Streamlined Forensic Reports (SFR). These staged reports allow key scientific conclusions to be shared early in the process, helping defence and prosecution to identify disputed issues and target further analysis efficiently.

• An SFR1 report summarises initial findings and allows the defence to decide if the evidence is accepted;
• If disputed, a more detailed SFR2 report will address specific contested points, leading to a full expert report if necessary.

This staged approach can reduce trial length and focus forensic testimony on matters genuinely in dispute.

Challenges, Cross‑Examination and Weight of Evidence

Forensic evidence, once presented, is subject to rigorous examination by the opposing side. Lawyers may challenge:

• The methods used in analysis;
• The quality of laboratory procedures or controls;
• The expert's interpretation and conclusions.

In cross‑examination, experts may be asked to explain limitations, uncertainties or alternative explanations. The judge or jury then assesses the weight of the evidence - how persuasive it is - in the context of all other evidence in the case.

Concerns about forensic practice have prompted calls for improved standards, greater training for experts, and stronger oversight to prevent wrongful convictions based on unreliable science. Recent reports highlight systemic issues within forensic provision in England and Wales and stress the need for robust, transparent scientific practices.

Practical Considerations for Parties

Defence and Prosecutors

Both sides must engage with forensic evidence early:

• Defence teams should seek full disclosure of reports and exhibits, and may instruct their own forensic experts to challenge or interpret findings;
• Prosecutors must ensure reports are comprehensive, compliant with standards, and disclosed in time for defence review. Progressing forensic evidence without adequate preparation can lead to adjournments or weakened case strength.

Jury and Judge

Judges may give directions on the interpretation of scientific evidence to juries, emphasising that conclusions depend on reliable methods and expert integrity. Clear, accessible presentation helps lay jurors avoid misunderstanding complex science.

Key Takeaways

In criminal trials in England and Wales, forensic evidence is presented through a structured process that combines scientific rigour with legal requirements. Forensic specialists produce written reports compliant with regulatory standards, which are disclosed to all parties before trial. In court, experts explain findings under oath, are examined and cross‑examined, and their evidence is weighed alongside other material. Recent regulatory reforms aim to strengthen quality and transparency. A clear grasp of how forensic evidence is presented and scrutinised helps all participants navigate complex trials fairly and effectively.

James William Steven Parker

James is the founder of UKLegalGuides.com and a former agent at the Ministry of Justice (UK). With a background in processing legal claims, he launched this platform to make the laws of England and Wales accessible to everyone.