Forensics
If the chain of custody is broken, is the evidence thrown out?
Not automatically, and the assumption hides two different questions. Integrity asks whether the item is what it is said to be; admissibility asks whether the law lets a court receive it. A system can answer one yes and the other no.
In short
Two questions get asked about an item of evidence and they are constantly confused. The first is whether the thing in the courtroom is the thing that was found, unaltered and correctly attributed — that is integrity, and chain of custody is the record that supports it. The second is whether the law permits a court to receive it at all — that is admissibility, and it turns on rules that have nothing to do with whether the item is genuine.
Why it exists
AnalysisA forensic result is only about the item that was examined. If the item examined was not the item recovered — mislabelled, substituted, contaminated, or simply not traceable back — then the result is a true statement about the wrong thing. Everything the discipline does afterwards rests on a question answered before the science starts.
How it works
AnalysisIntegrity is a continuity question. The record supporting it accounts for who held an item and when, from recovery through examination to presentation, so that the item examined can be tied to the item recovered. It is documentation rather than analysis, and it is produced by everyone who touches the item rather than by the laboratory alone.
That is why the regulatory scheme in England and Wales is drafted to reach beyond laboratories. The Forensic Science Regulator’s stated priority is that quality standards apply equally whether services are delivered by small or large organisations, private companies, public laboratories, police forces or individuals — and that compliance runs from crime scene to court and in all sectors.
Failures of integrity are handled evidentially rather than by exclusion. Under the Forensic Science Regulator Act 2021 a failure to act in accordance with the code does not of itself make a person liable to civil or criminal proceedings — but the code is admissible in criminal and civil proceedings, and a court may in particular take a failure into account in determining a question in such proceedings. The consequence is that the evidence is worth less, decided by the body deciding the case.
Admissibility is a separate gate with separate keys. In England and Wales the reliability question reaches the court through the expert’s report, which must include such information as the court may need to decide whether the expert’s opinion is sufficiently reliable to be admissible as evidence — a requirement directed at the opinion rather than at the item.
Contamination shows why integrity is a scientific problem and not only a bureaucratic one. The final NIST review of DNA mixture interpretation records that people constantly shed small amounts of DNA into the environment and can transfer small amounts, including someone else’s, from one surface to another — and that among the interpretive difficulties is determining whether detected DNA is relevant to the crime being investigated or is from contamination.
Common misconceptions
Widely held beliefs that do not match how the system actually operates.
Common belief: A break in the chain of custody means the evidence is thrown out.
In practice: Integrity and admissibility are different questions. Under the English regulatory scheme a failure to follow the code is not itself an offence; the code is admissible and a court may take the failure into account when determining a question — which is about weight, not automatic exclusion.
Common belief: If an item is properly documented, it will be admitted.
In practice: Admissibility turns on rules about how material was obtained and what it is offered to prove, which are unconnected to whether the item is genuine. A perfectly documented item can be inadmissible.
Common belief: Chain of custody is a laboratory matter.
In practice: The English regulator’s stated priority is compliance from crime scene to court and in all sectors, applying equally to private companies, public laboratories, police forces and individuals. Most of the chain happens before the laboratory.
Common belief: Contamination is a handling failure rather than a scientific issue.
In practice: The NIST review identifies determining whether detected DNA is relevant to the crime or is from contamination as one of the interpretive difficulties with mixtures. It is a question the interpretation has to confront, not only a question about procedure.
How this varies between jurisdictions
A required section on every guide. Arrangements differ between countries, and we say how.
Three distinct mechanisms, frequently described as one.
- Continuity of the item — the documented account of who held it and when, produced by everyone who handled it.
- Quality of the activity — regulated from crime scene to court and across all sectors, with an evidential rather than penal sanction (England and Wales).
- Admissibility of the opinion — a legal gate the expert’s report must supply the court with material to pass (England and Wales, CrimPR r. 19.4(h)).
Rights and accountability
AnalysisThe continuity record is one of the few parts of a forensic case a non-scientist can examine. It does not require expertise in the method to ask who held an item and when, which makes it a practical route for testing evidence that is otherwise difficult to challenge from outside the discipline.
That is also why documented standards matter more than assurances. Where the code is admissible and the report must state the expert’s accreditation, the defence has something written to measure the work against, rather than a conclusion to disbelieve.
What we could not establish
- Admissibility rules differ in every jurisdiction and none is set out here. This page describes the distinction between two questions, not the law of evidence in any system.
- Nothing here describes collection, packaging, storage or transfer procedures, and nothing here describes how any control could be affected.
Where to go next
Related: chain of custody, expert evidence in court, and what a criminal investigation is. Whether there was legal authority to examine an item in the first place, and whose competence that is, is device seizure and device examination.
Related topics
- Whose expert is the expert?
Two systems answer that differently and both are answering the same worry — that an expert paid by one side will start arguing for it. Germany removes the party from the choice: the judge selects the expert. England and Wales keeps the party and subordinates the loyalty.
- What does a DNA result actually tell you?
Less than the phrase "DNA evidence" suggests, and one legal system says so in statute — listing what a molecular-genetic examination may determine and providing that other findings may not be made at all.
- What is a criminal investigation?
A criminal investigation is a legally authorised process for establishing whether an offence occurred and gathering evidence that can be tested in court. This guide explains its structure, safeguards, and known failure modes.
- Is evidence obtained unlawfully always thrown out?
Three constitutions answer this in two different ways. Brazil states inadmissibility flatly. South Africa and Kenya make exclusion conditional on what admitting the evidence would do to the trial — which means the violation alone does not decide it.
Sources
Forensic Science Regulator Act 2021 (2021 c. 14), sections 1 to 7
The National Archives (legislation.gov.uk) · Legislation · 2021 · link verified 2026-08-26
The official revised text, each section read directly at its own page. Supports s. 1: "There is to be a Forensic Science Regulator" (in force 25 July 2022, S.I. 2022/856). Supports s. 2: the Regulator must prepare and publish a code of practice about the carrying on of forensic science activities in England and Wales; the code must specify the activities it applies to, need not make provision about every forensic science activity, and may make different provision for different purposes or descriptions of person; the Regulator must keep it under review. Supports s. 3: before publishing the code or alterations the Regulator must consult, including persons representative of those carrying on the activities, and may not publish unless a draft has been sent to the Secretary of State, the Secretary of State has approved it and laid it before Parliament, and the draft has been approved by a resolution of EACH HOUSE of Parliament. Supports s. 4, headed "Status of the code": "A failure by a person to act in accordance with the code does not of itself make that person liable to civil or criminal proceedings"; "The code is admissible in evidence in criminal and civil proceedings in England and Wales"; and "A court may in particular take into account a failure by a person to act in accordance with the code in determining a question in any such proceedings." Supports s. 5: the Regulator may investigate where it has reason to believe a person may be carrying on a forensic science activity to which the code applies in a way that creates a substantial risk of adversely affecting any investigation or impeding or prejudicing the course of justice, and may require documents and other information by written notice. Supports s. 7: completion certificates following a compliance notice under s. 6, with a 14-day period to respond to an application. This is the law of ENGLAND AND WALES — the provisions are extent-marked "E+W". It supports nothing about Scotland or Northern Ireland, which have separate arrangements, and nothing about any other country. It establishes no scientific claim about any forensic method.
Forensic Science Regulator — About us
Forensic Science Regulator (GOV.UK) · Government publication · link verified 2026-08-26
The Regulator's own account of itself, read directly. Supports: that the Regulator "ensures that the provision of forensic science services across the criminal justice system is subject to an appropriate regime of scientific quality standards"; that the Forensic Science Regulator Act 2021 provided powers to investigate and take enforcement action where there are substantial risks to criminal investigations or proceedings; that its responsibilities involve identifying the requirement for new or improved quality standards, leading on their development, and providing advice and guidance so providers can demonstrate compliance; and that its priorities include appropriate quality standards for all forensic science disciplines "which apply equally whether the services are delivered by small or large organisations, private companies, public laboratories, police forces or individuals" and compliance "from crime scene to court and in all sectors". Cited for the STRUCTURE of forensic provision in England and Wales — mixed rather than unified — and attributed as the Regulator's own statement. It supports no claim about compliance levels, quality, or any other country.
The National Archives (legislation.gov.uk) · Legislation · 2025 · link verified 2026-08-26
The official text of the current Rules, read directly. NOTE ON CURRENCY: the Criminal Procedure Rules 2020 (S.I. 2020/759) were REVOKED with effect from 6 October 2025 by these Rules; the 2020 text was fetched first and legislation.gov.uk records it as revoked, so the 2025 Rules are cited instead. Supports r. 19.1: the Part applies where a party wants to introduce expert opinion evidence, and an "expert" means a person required to give or prepare expert evidence for the purpose of criminal proceedings, including evidence required to determine fitness to plead or for the purpose of sentencing. Supports r. 19.2: "An expert must help the court to achieve the overriding objective" by giving opinion which is "objective and unbiased" and "within the expert's area or areas of expertise", and by actively assisting the court in its case-management duty; r. 19.2(2): "This duty overrides any obligation to the person from whom the expert receives instructions or by whom the expert is paid"; r. 19.2(3): obligations to define the expert's area of expertise in the report and when giving evidence, to draw the court's attention to any question whose answer would be outside that area, and to inform all parties and the court if the expert's opinion changes. Supports r. 19.4, the required content of an expert's report, including: qualifications, relevant experience and accreditation (a); the literature or other information relied on (b); the substance of all material facts given to the expert (c); where there is a range of opinion, a summary of that range and reasons for the expert's own opinion (f); any qualification the expert must attach to an opinion (g); "such information as the court may need to decide whether the expert's opinion is sufficiently reliable to be admissible as evidence" (h); a summary of conclusions (i); a statement that the expert understands and has complied with the duty to the court (j); and the same declaration of truth as a witness statement (k). Rules in force 6 October 2025. ENGLAND AND WALES only, extent-marked "E+W". It supports nothing about Scotland or Northern Ireland, nothing about civil proceedings, and no claim about how any court weighs expert evidence in practice.
National Institute of Standards and Technology (United States) · Government publication · 2024-12 · link verified 2026-08-26
The FINAL report, retrieved as the primary PDF from the NIST publications server and text-extracted locally; the executive summary was read in full. The June 2021 draft (NISTIR 8351-DRAFT) was fetched first and is NOT used — a draft is not authority for a load-bearing claim. Supports, verbatim: "All scientific methods have limits. To use a method appropriately, one must understand those limits, which are inevitably tied to the risk one is willing to accept either as an individual or as a society." Supports the account of increased sensitivity: in the 1990s an evidence sample needed to contain thousands of cells, such as from a visible blood or semen stain, whereas analysts can now extract a DNA profile from the few skin cells someone might leave when handling an object. Supports that "people constantly shed small amounts of DNA into the environment" and can transfer small amounts, including someone else's DNA, from one surface to another. Supports that highly sensitive methods often detect DNA from more than one individual, and that it can be difficult to distinguish one person's DNA from another in mixtures, to estimate how many individuals contributed, to determine whether the DNA is relevant to the crime or is from contamination, and to determine whether there is a trace amount from the suspect or victim. Supports the central comparative finding: for high-quality single-source samples "it has been demonstrated that different laboratories will arrive at the same result … regardless of the specific instruments, tests, and software used", whereas "multiple interlaboratory studies conducted by different groups over the past two decades have demonstrated that different laboratories can produce a wide range of results when interpreting the same DNA mixtures". A United States federal scientific review. It supports no claim about practice in any other country, no claim about any individual case, and no legal conclusion.