What Is a Chain of Custody for Evidence?

Just because a party offers evidence in a criminal case doesn't mean the judge will allow it. The offered evidence must comply with several rules before a judge will admit it into the case. One such rule is that a party seeking to offer a tangible object as evidence must establish an unbroken and reliable "chain of custody."

What Is a Chain of Custody for Evidence?

The chain of custody shows the path the evidence took from the crime scene (or elsewhere) to the courtroom to ensure it's what the party says it is and it hasn't been tampered with. For example, if a prosecutor in a murder case wanted to introduce a knife found at the crime scene, they'd have to establish a chain of custody to prove that it was in fact the knife found at the scene and not some other knife. In legal terms, the chain of custody authenticates the evidence. (Fed. R. Evid. 901.)

Why Chain of Custody Matters in a Criminal Case

The chain of custody works to ensure the evidence is what it purports to be, has not been tampered with or altered, and has been appropriately handled and tested. Without such measures, judges and juries might base a conviction on planted evidence, inaccurate test results, or an item that was never at the crime scene.

When Is Chain of Custody Required?

Before evidence can be used in court, the party offering it must be able to show, step by step, who handled it and how it was protected from the time it was found until trial.

Evidence Requiring a Chain of Custody

The parties at a trial or hearing usually have to establish a chain of custody for the exhibits they want to introduce. Exhibits are tangible objects that are relevant to the facts of a case. Here are a few examples:

• a stolen cellphone in a shoplifting case
• the drugs in an illegal possession of controlled substances trial
• the photograph of a broken window in a burglary case, or
• the printout of a breathalyzer machine in a drunk driving prosecution.

In some cases, the physical evidence won't be introduced at trial. Rather it will be a forensic analysis or expert report regarding the evidence, such as a DNA analysis of a hair sample taken from the victim's clothes. A similar chain of custody must be established to prove the item analyzed was the item at issue.

Links in the Chain

Proving that an exhibit is exactly what it purports to be—the actual drugs found on the defendant or the very cellphone stolen from the store—requires proof of who had possession of the exhibit at all times between the time officers seized it and the trial.

Because criminal prosecutions typically depend on evidence gathered by police officers, it is prosecutors who generally need to establish a chain of custody. The prosecutor must identify where and who had the evidence from the time it left the crime scene to the time it arrived in the courtroom or at the lab. The length of the chain could be one person or multiple people. The prosecutor must go link by link to account for its continuous custody and unchanged condition.

How Chain of Custody Is Documented

Law enforcement agencies and prosecution offices generally have written policies that dictate how investigators and employees must collect, document, and store evidence—whether it's from a crime scene or digital evidence. Larger agencies might have an investigations unit or evidence and property unit that focus on these tasks.

Common Documentation of the Evidence Chain

Chain of custody procedures will vary depending on the type of evidence collected. But generally speaking, documentation should include the agency involved, a case number, description of the evidence, who collected the evidence, what collection procedures were used, who transported the evidence and how, and where and how the evidence is stored. Any person, agency, or entity that takes custody of the evidence will need to repeat this documentation.

Chain-of-Custody Example (Jane's Drug Case)

Let's assume that Jane is on trial for possession of cocaine. To prove Jane guilty, the prosecutor must establish that the substance in her possession was in fact cocaine. The prosecutor offers as evidence the packet of powder that a police officer removed from Jane's pocket. The prosecutor also offers evidence that scientific testing proved that the powder in question is cocaine.

To establish the chain of custody for the packet, the prosecutor must:

• show that the officer who seized the packet marked it in a way that makes it distinguishable from similar items that were taken from other suspects
• prove that the police transported and stored the packet in a way that provides reasonable assurance that nobody tampered with it
• call a qualified expert to testify to the chemical composition of the contents of the packet
• establish that the packet given to and tested by the expert is the one that the officer seized from Jane, and
• prove that the packet the expert tested is the same packet that the police have brought to the trial.

Taken together, these steps show the judge that the evidence in Jane's case is the same packet seized at the scene, has been handled carefully, and can be trusted as the basis for any verdict.

What Happens If the Chain of Custody Is Broken?

A gap in the chain of custody can lead to problems for the party trying to offer the evidence. While a perfect chain of custody is not required for an item to be admitted into evidence, gaps or missteps will make the party's job more difficult. For a prosecutor, they must convince the judge to let the evidence in and convince the jury beyond a reasonable doubt that the evidence is reliable.

Standard of proof. The party offering the evidence needs to make a sufficient showing on its face that the evidence is what it claims to be and is in substantially the same condition as when it was first obtained. The law even gives prosecutors and law enforcement the benefit of the doubt when it comes to discharging their duties properly. (U.S. v. Lott, 854 F.2d 244 (7th Cir. 1988).)

Gaps in the chain. Any minor gaps in the chain or possible mishandling generally go to the weight of evidence, which is decided by the jury. But, if an entire link is missing, the judge might very well exclude the evidence unless the prosecution can find another way to establish that the evidence is what it purports to be and hasn't been tampered with.

How Defendants Challenge Chain of Custody in Court

Most often, the defense will be in the position of challenging the chain of custody. A typical defense strategy is to attack the sufficiency of the prosecutor's chain—link by link. The defense might do this by showing an irregularity or discrepancy in the timeline or documentation, or challenging how the item was stored, labeled, or tested. If the defense succeeds in preventing the prosecutor from offering an exhibit into evidence, the judge might rule that the prosecutor has insufficient evidence to allow a case to continue. (That determination rests on how crucial the piece of evidence is to the case.)

Going back to Jane's example, her attorney can challenge each and every step in the seizure-storage-testing-transportation process. If the prosecutor cannot convince the judge that the foundation is adequate, the judge will rule the packet inadmissible and, in all probability, dismiss the case.

Frequently Asked Questions on Chain-of-Custody Issues

Below are answers to a few commonly asked questions regarding chain-of-custody issues.

• Is chain of custody the same as evidence handling?
• Can a case be dismissed over chain of custody?
• Does chain of custody apply in civil cases?

Is chain of custody the same as evidence handling?

No. Chain of custody is the documented record of who had the evidence and when, while evidence handling is the broader process of collecting, storing, testing, and presenting that evidence. Chain-of-custody issues go to the evidence's authenticity.

Can a case be dismissed over chain of custody?

Yes, in some situations a serious problem with the chain of custody can keep key evidence out of court, and if that evidence is crucial, the judge or prosecutor may have to drop the charges or dismiss the case.

Does chain of custody apply in civil cases?

Yes. Chain of custody principles also apply in civil cases (like lawsuits over medical tests, product defects, or digital records) to show that important evidence has been kept secure and unchanged.