Rules of Evidence Governing Physical and Demonstrative Exhibits

Why Rules of Evidence Matter to the Forensic Technician

Everything you collect, package, label, and analyze at a crime scene ultimately serves one purpose: to be presented in court. A fingerprint card that is perfectly developed but cannot be admitted into evidence is useless to a prosecution or defense. Understanding the legal rules that govern admission of physical and demonstrative exhibits is therefore a core professional competency — not a lawyer's problem.

The Federal Rules of Evidence (FRE) provide the framework used in all federal courts and serve as the model for most state evidence codes. Even if you work in a state court, the underlying concepts are nearly identical. This lesson focuses on four foundational requirements: relevance, authentication, the best-evidence rule, and chain of custody.

Relevance: The First Gate

Before any exhibit reaches a jury, the offering party must show it is relevant. Under the plain-language meaning of FRE 401, evidence is relevant when it makes a fact that matters to the case more or less probable than it would be without the evidence. A bloody glove found at the scene is relevant to a homicide. A gas receipt from two weeks before the crime may not be.

As a technician, you are not the judge of relevance — the attorney and judge decide that. Your job is to collect and document everything that could conceivably matter so that lawyers have the full picture. Under-collection cannot be corrected later; over-collection can be narrowed.

Authentication: Proving the Item Is What It Claims to Be

FRE 901 requires that the proponent of evidence produce enough proof that the item is what it is claimed to be. For a forensic technician, this means you must be able to testify — clearly and specifically — that the item in court is the same item you collected, handled, or analyzed.

Authentication is accomplished through:

• Personal knowledge — you collected the item and can identify it by unique markings (your initials, a case number, date, and location written directly on the item or its packaging).
• Distinctive characteristics — unusual features, serial numbers, or lab markings that make the item identifiable.
• Chain of custody documentation — a continuous, documented record showing every person who had possession of the item, when they received it, and when they transferred it.

For photographs, authentication means testifying that the photograph accurately and fairly depicts the scene or object as it appeared at the relevant time. You do not need to have taken the photograph yourself; you need to have personal knowledge of the scene so you can confirm accuracy.

Chain of Custody: The Backbone of Authentication

Chain of custody is a documented, unbroken sequence of possession from the moment an item is collected through its presentation in court. Every transfer must be recorded: collector, packaging officer, property room technician, lab analyst, and anyone else who touched the item.

A gap in the chain does not automatically exclude evidence, but it gives opposing counsel grounds to challenge the item's integrity and creates reasonable doubt in the minds of jurors. Your responsibility is to make the chain as tight and complete as possible:

1. Mark or seal the item immediately upon collection.

2. Complete a property/evidence log entry at the scene.

3. Transfer using a signed receipt or electronic log entry.

4. Never leave evidence unsecured or with an undocumented person.

Safety note: When handling biological evidence or items with sharp edges, always wear appropriate PPE (nitrile gloves, cut-resistant gloves as needed) before touching or packaging. Contamination is both a health hazard and an evidence-integrity problem — a compromised sample may be excluded on authentication grounds.

The Best-Evidence Rule

FRE 1001 and its related provisions state that when the content of a writing, recording, or photograph is at issue, the original is required. Practically, this means:

• The original crime-scene photograph (or a certified digital duplicate) should be offered, not a photocopy of a printout.
• Original laboratory reports or certified copies are required; a technician reading from memory is insufficient.
• Chain-of-custody forms are themselves documents subject to this rule — originals or certified copies matter.

Modern digital evidence has complicated this slightly. Courts have generally accepted that a proper forensic duplicate (a verified, bit-for-bit copy with a matching hash value) satisfies the original requirement for digital files. Understanding this distinction becomes critical when you work with surveillance footage, cell-phone extractions, or computer forensic evidence.

Laying Foundation in the Witness Chair

When you take the stand, the attorney presenting your evidence will ask you a series of foundational questions before the exhibit is formally admitted. A typical foundation for a latent-print card might sound like:

1. Were you present at the crime scene on the date in question?

2. Did you collect an item of evidence there?

3. Can you describe how you marked it?

4. Is this the item you collected? How do you know?

5. Has it been in your care or in secure property storage since collection?

6. Does it appear to be in the same condition as when you collected it?

Your answers must be truthful, specific, and based on personal knowledge. If you do not know something — for example, whether the item was tested by another analyst — say so. Overstating your knowledge is a serious professional and legal error.

Demonstrative Exhibits: A Special Category

Demonstrative exhibits — diagrams, courtroom-scale models, computer animations, or enlarged photographs — are not the actual evidence but are used to help the jury understand it. These must be shown to be a fair and accurate representation of the real evidence or scene. You may be asked to testify that a diagram you drew is to scale or that a photo enlargement has not been altered. Accuracy in your original documentation makes this straightforward; sloppy original work can make demonstratives impossible to authenticate.