The days are gone when courts took juries on expensive field trips to the crime scene. Today, just about anything they need to see can be accomplished with the use of exhibits, models, reconstructions, videotapes, and animations. Almost anything "visual" ("sound" still enjoys certain Fifth Amendment protections) can be presented in modern courts (under certain rules) and the effects are dramatic since people retain 87% of what they see and only 10% of what they hear.
Exhibits generally fall into one of two (2) categories: (1) real evidence; or (2) demonstrative evidence.
Real evidence is evidence that speaks for itself, as when the prosecutor holds up a bag containing the murder weapon, asks the police officer "Is this the weapon you found?", and then enters it as "Exhibit A". Even though it is authenticated by a witness, real evidence is separate, distinct, and doesn't rely upon a witness' testimony. It has the weight of being additional evidence and can serve many purposes.
Demonstrative evidence is evidence that illustrates or helps explain oral testimony, or recreates a tangible thing, occurrence, event, or experiment. Scientific evidence falls into this category, as when a toxicologist testifies that the victim died of lead poisoning and refers to a chart of the human body showing the circulatory pathways that the toxin traveled. Visual aids of this type are intimately tied to the credibility of the witness who testified with them, and although they are not separate pieces of evidence, like real evidence, a jury can usually view them again while it deliberates.
Here's a list of some (not all) of the things that can be used as demonstrative evidence:
plaster casts or molds
maps, charts, diagrams, and drawings
police composites, mug shots, sketches
computer reconstruction or animation
scientific tests or experiments
(1) The most general rule is that there must be some other piece of evidence -- a fact, an object, or testimony -- that needs to be illustrated or demonstrated. Presentation is actually a two-stage process: first some issue of fact, then the explanation or demonstration stage. Demonstrative evidence is intended to be an adjunct to testimony.
(2) The next most general rule involves the foundational requirements for demonstrative evidence. Certain preliminary steps must be followed such as authentication and accuracy. This is known as "laying the foundation" and is mandatory whenever any scientific expertise is about to be forthcoming. Foundational requirements (other than those dealing with the expertise of the person) usually involve:
authentication -- the demonstrative evidence should convey what it is meant to convey. What it conveys must not alter, distort, or change the appearance or condition of something in any significant way. A computer enhanced photograph, for example, to make a crime scene area look lighter than it actually was is probably inadmissible. There are specific rules, however, that do allow computer enhancements under some circumstances.
representational accuracy -- the demonstrative evidence should fairly depict the scale, dimensions, and contours of the underlying evidence. A photograph or chart with some small section of it enlarged to focus in on is probably inadmissible. This is followed rigorously whenever comparisons (such as between two samples of handwriting) are made so that any lay person can compare the evidence oculis subjecta fidelibus.
identification -- the demonstrative evidence must be an exact match to the underlying evidence or the testimony illustrated. This requirement is the same as with real evidence. For example, an expert witness is about to testify using a enlarged photograph (to scale) clearly showing the outline of a bootprint with a unique manufacturer mark on the bottom of it. The victim (or police officer if the victim didn't survive) who was boot-stomped by it must identify that mark as the one that boot-stomped her.
|Note: It's often said that demonstrative evidence inherently favors the prosecution, and for two reasons. One, there's usually NO stipulation allowed. A stipulation is when either side gives up on some issue at some point in trial and says "We'll stipulate that our client owns a boot with that particular mark, your Honor" for example. Instead, the defense, who might want to move the trial along has to suffer through a long, drawn-out, embarrassing, and potentially damaging situation. Two, usually along with the process of laying the foundation for demonstrative evidence, the jury also gets to look at what is being authenticated, represented, or identified. If an objection to the foundation (or later challenge for prejudice) is successful, the exhibit is taken down, but the impression remains on the minds of the jurors, even if the judge instructs the jury to disregard it. This is called jury view, and some attorneys consider it to have certain tactical advantages. It's also one of the reasons why pretrial Frye or Daubert hearings are so important.|
(3) The next most general rule is that demonstrative evidence must pass the "three hurdles" of admissibility: relevancy; materiality; and competency (Mandatory reading: Lecture on Objections). Despite some disagreements over the precise meaning of these terms, relevancy means the demonstrative evidence has something to do with the reason the trial is being held, a point at law, a question of guilt or innocence, etc. Materiality means it goes directly to the purpose of illustration, is easily understandable, produces no wayward inferences, and is not just an exercise in "educating" the court or jury. Competency means it's the kind of thing that fits with the decor and decorum of the court, is on the up-and-up, ethical, and doesn't taint the court or subvert the justice process.
(4) The last most general rule is that demonstrative evidence must pass an additional balancing test for relevancy -- a weighing of what is probative/prejudicial. Probative is what is relevant to "cinch" the case for the prosecution by anticipating all defenses. Prejudicial is whatever inflames the passions and prejudices of the jury. This rule necessarily favors the defendant, in rooted in the principle of fundamental fairness, and protects them from unwarranted inferences about bad character or habit.
It's important to understand that the weighing of what probative/prejudicial varies with each and every case, and is not an arbitrary standard. It should NOT be referred to as the "gruesomeness" standard, as it sometimes is called. The mere fact that a photograph, for example, shows a shocking crime scene does not automatically make it gruesome or inflammatory. The courts have also ruled that a photo of a nude, bloodstained body is not inadmissible, but innocuous. Autopsy photos are another matter, and depend upon how much cutting and opening the forensic physician has made. In each case, the intent, principal value or effect of the evidence is to be judged as prejudicial, not so much the evidence itself. An extension of this makes it prejudicial error to dwell unnecessarily long on such evidence.
These are more like guides to judicial discretion than specific rules, and involve established practices or procedures for the presentation of various types of demonstrative evidence. In this respect, practices may vary considerably by jurisdiction.
(1) Plaster casts, molds, and models -- these are most admissible when viewable in all dimensions. Three-dimensional is always better than two-dimensional. Whatever construction material is used doesn't matter. Models of the crime scene are a regular feature of trials, and models that are not precisely to scale will also sometimes be admitted if they are professionally made and presented. An attorney, for example, cannot take a Styrofoam head and stab a knife through it in order to demonstrate the attack on the victim. Further, no one is usually allowed to play around with the models, and this is what was mostly involved in the controversy over anatomically correct dolls in the late 1980s.
(2) Maps, diagrams, sketches, and charts -- it's generally not important that the original creator of a map testify, only that whatever used is "official". Police-generated sketches and diagrams fall generally within judicial discretion where accuracy is the main concern. Sometimes, the evidence is taken as hearsay, or falls under one or more hearsay exemptions. A lot depends on the conditions of fairness and reliability at the time the sketch or diagram was made. Charts are viewed as useful adjuncts to testimony or not.
(3) Photographs -- the broad use of photographs is permitted. The photo must substantially and accurately depict the subject matter, and not be unduly prejudicial. Photos that support only one party's theory, or a small part of a theory, are considered self-serving and untrustworthy. Examples of such inadmissible evidence would be staged or posed photos. Some courts place limits on lens, filters, color, and other special equipment, but not many.
(4) Enlargements -- some courts place limits on the magnification allowed, no more than twenty power, for example. Photographs taken through microscopes depend upon the standardized criminalistics of the crime lab for a state or region.
(5) Videotapes -- videotaped depositions and confessions are becoming common, and in civil cases, the practice of a "day-in-the-life" video is often admitted. The practice of taping drunk drivers is also popular in some states, but is best considered as real, rather than demonstrative, evidence. Courts have upheld surveillance imagery of the perpetrator in action at the scene of the crime. With demonstrative evidence involving motion, each "frame" or specified number of milliseconds is considered a separate piece of evidence. In other words, a movie is treated as a series of still photographs since the courts are more comfortable and familiar with still photography. Any audio portion of a videotape cannot be played (due to 5th Amendment concerns), or if it is, requires separate authentication.
(6) Computer reconstruction -- reconstructionists are a fast-growing forensic specialty, and the expertise involves a projection of possible outcomes mathematically predicted by a computer program. For example, known facts such as weight, physical dimensions, and surface friction are plugged into a computer algorithm to generate an accident simulation. It must be shown the simulation (algorithm) is based on accepted principles of physics, and there are sometimes further requirements involving the credentials of the expert.
(7) Scientific tests/demonstrations -- if a laboratory test is performed in front of the judge and jury, the benefit is that jurors would be allowed to draw independent inferences from it rather than being warned by the judge later that they are free to disregard the scientific testimony. The standard, therefore, is substantial similarity. The expert presenting a test, upon being qualified, is assumed to represent the theory of virtual certainty that the test would yield consistent results if replicated under substantially similar conditions. However, cross-examination of such experts is notoriously fierce.
Craig Ball's Ten Commandments of Demonstrative Evidence
A Law Firm's Guide to the Law of Demonstrative Evidence
The Visual Evidence Center's Chart on Planning Demonstrative Evidence
Kantor, T. (1998) Winning Your Case with Graphics. Boca Raton: CRC Press.
Koppenhaver, K. (1996) Demonstrative Evidence. MO: Forensic Publishers of Joppa.
Moenssens, A., J. Starrs, C. Henderson & F. Inbau (1995) Scientific Evidence in Civil and Criminal Cases. Westbury, NY: Foundation Press.
Siemer, D. (1984) Tangible Evidence: How to Use Exhibits at Trial. NY: Aspen Publishers.