What Is Chain of Custody? Definition and Examples

An evidence bag containing a blood sample
Evidence bag with blood sample. Science Photo Library / Getty Images

In criminal and civil law, the term “chain of custody” refers to the order in which items of evidence have been handled during the investigation of a case. Proving that an item has been properly handled through an unbroken chain of custody is required for it to be legally accepted as evidence in court. While often unnoticed outside the courthouse, proper chain of custody has been a crucial factor in high-profile cases, such as the 1994 murder trial of former professional football star O.J. Simpson.

Key Takeaways

  • Chain of custody is a legal term referring to the order and manner in which physical or electronic evidence in criminal and civil investigations has been handled.
  • In criminal trials, the prosecution must typically prove that all evidence was handled according to a properly documented and unbroken chain of custody.
  • Crime-related items found not to have followed a properly documented and unbroken chain of custody may not be allowed as evidence in trials.

Chain of Custody Definition

In practice, a chain of custody is a chronological paper trail documenting when, how, and by whom individual items of physical or electronic evidence—such as cell phone logs—were collected, handled, analyzed, or otherwise controlled during an investigation. Under the law, an item will not be accepted as evidence during the trial—will not be seen by the jury—unless the chain of custody is an unbroken and fully documented trail without gaps or discrepancies. In order to convict a defendant of a crime, the evidence against them must have been handled in a meticulously careful manner to prevent tampering or contamination.

In court, the chain of custody documentation is presented by the prosecution in order to prove that the item of evidence is, in fact, related to the alleged crime, and that it had been in the possession of the defendant. In an effort to establish a reasonable doubt of guilt, the defense looks for holes or acts of mishandling in the chain of custody to show, for example, that the item may have been fraudulently “planted” to make the accused person appear guilty.

In the O.J. Simpson trial, for example, Simpson’s defense showed that crime scene blood samples had been in the possession of multiple investigating officers for various lengths of time without being properly recorded on the Chain of Custody Form. This omission enabled the defense to create doubt in the minds of the jurors that blood evidence linking Simpson to the crime could have been planted or contaminated in order to frame him.

From the time it is collected until it appears in court, an item of evidence must always be in the physical custody of an identifiable, legally-authorized person. Thus, a chain of custody in a criminal cased might be:

  • A police officer collects a gun at the crime scene and places it in a sealed container.
  • The police officer gives the gun to a police forensics technician.
  • The forensics technician removes the gun from the container, collects fingerprints and other evidence present on the weapon, and places the gun along with the evidence collected from it back into the sealed container.
  • The forensics technician gives the gun and related evidence to a police evidence technician.
  • The evidence technician stores the gun and related evidence in a secure place and records everyone who accesses the evidence during the investigation until final disposition of the case.

Items of evidence are typically moved in and out of storage and handled by different people. All changes in the possession, handling, and analysis of items of evidence must be recorded on a Chain of Custody Form.

Chain of Custody Form

The Chain of Custody Form (CCF or CoC) is used to record all changes in the seizure, custody, control, transfer, analysis, and disposition of physical and electronic evidence. A typical Chain of Custody Form will describe the evidence and detail the location and conditions under which the evidence was collected. As the evidence proceeds through the investigation and trail, the CCF must be updated to show at a minimum:

  • The identity and signature of each person who handled the evidence and their authority to do so.
  • How long the evidence was in the possession of each person who handled it.
  • How the evidence was transferred each time it changed hands.

The Chain of Custody Form may be handled only by identifiable persons with authority to possess the evidence, such as police officers and detectives, forensic analysts, certain officers of the court, and evidence technicians.

To the prosecution in criminal cases, a complete and properly completed Chain of Custody Form is essential in withstanding legal challenges to the authenticity of the evidence.

Chain of Custody in Civil Cases

While more commonly an issue in the criminal justice system, a chain of custody may also be required in civil cases, such as lawsuits arising from impaired driving incidents and acts of medical malpractice.

For example, victims of traffic crashes caused by uninsured drunk drivers must often sue the offending driver for damages in civil court. In such cases, the injured plaintiff will need to show evidence of the defendant driver’s positive blood-alcohol test following the accident. To prove the validity of that evidence, the plaintiff will need to show that the defendant’s blood samples followed an unbroken chain of custody. Lack of a satisfactory chain of custody could prevent the blood test results from being considered as evidence in court.

Similarly, in medical malpractice cases, medical and hospital records handled through an unbroken chain of custody must be introduced as evidence.

Other Areas of Chain of Custody Importance

Apart from crime scene investigations and civil lawsuits, some clinical areas in which a well-maintained chain of custody is important includes:

  • The testing of athletes for the use of banned substances
  • The tracing of food products to ensure they are authentic and were ethically sourced
  • In research involving the use of animals to ensure the animals were ethically sourced and humanly treated
  • In clinical trials of new drugs and vaccines
  • In establishing provenance—proof of authenticity and timeline of the ownership and location of art, antiques, and rare documents, stamps, and coins
  • In tracing missing letters, parcels, or other postal products
  • In the procurement of drugs used for execution by lethal injection
  • In the seizure of valuable items by customs, income tax, or revenue departments

A chain of custody is particularly important in environmental sampling to establish accountability for contamination and the accidental release of hazardous waste. 

Sources and Further Reference

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Longley, Robert. "What Is Chain of Custody? Definition and Examples." ThoughtCo, Jul. 13, 2022, thoughtco.com/chain-of-custody-4589132. Longley, Robert. (2022, July 13). What Is Chain of Custody? Definition and Examples. Retrieved from https://www.thoughtco.com/chain-of-custody-4589132 Longley, Robert. "What Is Chain of Custody? Definition and Examples." ThoughtCo. https://www.thoughtco.com/chain-of-custody-4589132 (accessed June 10, 2023).