Case File 296 · Investigation Psychology

What Is Chain of Custody?

Chain of custody is the documented record that tracks a piece of evidence from the moment it is collected until it is presented in court. It logs every person who handled the item, when they received

By Murder Book Editorial TeamPublished by Gungrounds, the studio making Murder BookPublished 3 October 2026Updated 3 October 2026

Chain of custody is the documented record that tracks a piece of evidence from the moment it is collected until it is presented in court. It logs every person who handled the item, when they received it, what they did with it and how it was stored. If the chain is incomplete or poorly documented, a court may question whether the evidence is authentic, and in some cases may exclude it entirely. The concept applies to physical evidence such as weapons or biological samples, to documents, and increasingly to digital files. For investigators, maintaining chain of custody is not a formality; it is the mechanism that keeps evidence trustworthy.

Key takeaways

Chain of custody is the continuous, documented record of who handled a piece of evidence, when and under what conditions.
Its purpose is to show that evidence has not been tampered with, contaminated or substituted between collection and court.
In the United States, Federal Rule of Evidence 901 requires that the proponent of evidence produce enough proof for a reasonable juror to find the item is what it is claimed to be.
A break in the chain does not automatically exclude evidence, but it can weaken its credibility or lead to exclusion at the judge's discretion.
The Innocence Project has found that problems with forensic evidence, including handling issues, contributed to roughly half of DNA-based wrongful convictions.

Why does chain of custody matter?

Evidence is only useful in court if the jury can trust that it is genuine and unaltered. Chain of custody provides that trust. When an investigator collects a blood sample at a crime scene and it later undergoes DNA analysis, the chain of custody documentation lets the court verify that the sample tested in the laboratory is the same sample collected at the scene, and that nothing happened to it in between that could have changed the result.

Without that documentation, the defence can argue that the evidence may have been contaminated, switched or degraded. Even if the evidence itself is perfectly sound, the inability to prove its handling history can undermine an entire case. For a broader look at what makes evidence credible, see what corroborating evidence means and why corroboration matters in investigations.

What does a chain of custody record include?

A proper chain of custody log typically documents:

Who collected the item, including their name, role and signature.
When it was collected, with date and time.
Where it was found, described precisely enough to locate the spot.
How it was packaged, sealed and labelled.
Every transfer from one person or facility to another, with signatures and timestamps.
Storage conditions, such as whether it was kept in a locked room, a refrigerated unit or a sealed evidence bag.

In digital forensics, the National Institute of Standards and Technology (NIST) recommends additional safeguards such as cryptographic hash values, digital signatures and automated access logs to verify that electronic files have not been altered.

How does chain of custody relate to authentication?

In the United States, Federal Rule of Evidence 901(a) sets the standard for authentication. It requires "evidence sufficient to support a finding" that the item is what its proponent claims. The judge does not decide authenticity outright; instead, the judge decides whether there is enough evidence of authenticity for the question to go to the jury.

Chain of custody is one of the primary ways to satisfy this requirement for physical and digital evidence. By showing an unbroken record of handling, the proponent demonstrates that the item presented in court is the same item collected at the scene and that it has not been tampered with.

What happens when the chain is broken?

A gap in the chain of custody does not automatically make evidence inadmissible. In U.S. v. Grant (1992), the Second Circuit Court of Appeals held that a break in the chain "will not necessarily lead to the exclusion of the evidence." The key question is whether the authentication testimony is complete enough to make it improbable that the original item was exchanged or tampered with.

In practice, the trial judge has broad discretion. If a gap is minor and there is no indication of tampering, the evidence may be admitted, and the gap goes to the weight the jury gives it rather than its admissibility. If the gap is significant, or if there are signs that the evidence may have been compromised, the judge can exclude it.

This discretion matters because real investigations involve many people. A single piece of evidence might pass through the hands of a patrol officer, a crime scene technician, a laboratory analyst and a court clerk. Each handoff is a point where documentation must be accurate. For related discussion on how evidence is evaluated, see what it means to challenge evidence and how evidence admissibility works.

How have chain of custody failures contributed to wrongful convictions?

The Innocence Project reports that unvalidated or improper forensic science contributed to approximately 50% of wrongful convictions later overturned by DNA evidence. While not every forensic problem is a chain of custody failure specifically, evidence handling sits at the foundation of forensic reliability. If evidence is mishandled before it reaches the laboratory, even a sound analytical technique can produce a misleading result.

Most wrongful convictions involve more than one contributing factor. An eyewitness may misidentify someone, and in the same case a forensic analyst may present flawed testimony. When these factors combine with poor evidence handling, the risk of error compounds. Understanding chain of custody is part of understanding why direct and circumstantial evidence each require careful evaluation.

Does chain of custody apply to digital evidence?

Yes, and the challenges are different from those involving physical objects. A physical item such as a knife can be sealed in a bag and stored in a locker. A digital file can be copied, moved, edited or deleted without leaving any visible trace unless the right tools are in place.

For digital evidence, chain of custody documentation typically includes cryptographic hash values, which are mathematical fingerprints of a file's contents. If the hash of a file at collection matches the hash at analysis, the file has not been altered. NIST SP 800-86, a publication from the National Institute of Standards and Technology, outlines procedures for integrating forensic techniques into incident response workflows and recommends automated access logs, timestamps and digital signatures as part of the chain.

The rise of digital evidence has made chain of custody more complex, but the underlying principle remains the same: every step between collection and court must be documented well enough that the evidence can be trusted.

What can investigators do to protect the chain?

Practical steps include:

Limiting the number of people who handle evidence. Each additional handler is another link in the chain that must be documented.
Using tamper-evident packaging. Sealed bags with unique identifiers make it obvious if evidence has been opened.
Logging every interaction. Even viewing evidence in storage should be recorded with the person's name, date, time and reason.
Storing evidence in secure, controlled-access facilities. Temperature, humidity and access controls matter for biological evidence in particular.
Using standardised forms. Consistent documentation reduces the chance of missing information.

These steps are not just bureaucratic requirements. They exist because any gap in the record is a point where the defence can raise doubt about the evidence's integrity, and with good reason: the reliability of the entire case may depend on it.

How does chain of custody work in Murder Book?

Murder Book is an upcoming narrative interrogation game in development for PC (Steam) and mobile, with release currently planned for the end of Q2 2027. Development screenshots show an evidence board where players link statements and physical details to build or challenge a theory. While the game centres on interrogation rather than forensic procedure, the principle behind chain of custody, that evidence must be trustworthy before it can be used, runs through the same reasoning players apply when deciding which statements to trust and which connections hold up. For more on how evidence supports or undermines a theory, see whether one piece of evidence can support more than one theory.