Evidence: The Concept of 'Admissibility'

For evidence to get admitted in criminal trials, it must be relevant, material, and competent. This means the evidence must help prove or disprove some fact in the case. It doesn't need to make the fact certain, but at least it must tend to increase or decrease the likelihood of some disputed fact. Evidence is "competent" if it complies with certain traditional notions of reliability.

Once admitted as relevant evidence, the jury (factfinder) will determine the appropriate weight to give a particular piece of evidence. The Sixth Amendment guarantees the right to a jury trial. But a criminal defendant can waive this constitutional right and request a bench trial. Then, a judge presides over the case and becomes the trier of fact.

This article explores the four types of evidence. It also covers issues with the competency, admissibility, and reliability of different kinds of evidence.

What Is Legally Admissible Evidence?

Federal trial courts (in both criminal and civil cases) use the Federal Rules of Evidence (FRE) to determine the admissibility of evidence. Each state has developed its own rules of evidence that govern state court civil and criminal proceedings. The state rules closely follow the FRE.

A judge may exclude a relevant fact when its potentially damaging effects outweigh its usefulness. FRE 403 outlines situations where judges may exclude such evidence, including scenarios where the evidence will:

  • Create bias in the jury (unfair prejudice)
  • Confuse the issues at hand
  • Mislead the jury
  • Cause undue delay or waste of time
  • Needlessly present cumulative (repetitive) evidence

A trial judge will weigh the probative value of the evidence. This is the evidence's ability to make a fact more or less likely to be true. This is balanced against the danger of unfair prejudice.

Types of Evidence

Different types of evidence are available in a criminal case. The four primary forms of evidence are:

  1. Demonstrative evidence
  2. Documentary evidence
  3. Real evidence
  4. Testimonial evidence

Some rules of evidence apply to all four types, and some apply to one or two. The court must find these forms of evidence admissible before examining their probative value.

Demonstrative Evidence

Demonstrative or illustrative evidence is often presented in the form of objects. This type of evidence is for aiding witness testimony in explaining or highlighting a key fact. Common examples include the following:

  • Maps
  • Diagrams
  • Reconstructive models

Expert witnesses testify on complex issues and use demonstrative evidence to simplify technical terms and concepts. Certain evidence is so complicated, like DNA evidence, that it requires an expert witness to interpret and explain it to the court. For example, a blood analysis expert may use a crime scene diagram to explain irregularities in the blood spatter pattern.

The court will allow expert testimony after establishing the witness's expertise and whether the witness used reliable methods acknowledged within the scientific community. The object's admissibility depends on whether it's more probative than prejudicial. Learn more about demonstrative evidence and its admissibility.

Documentary Evidence

Documentary evidence covers many papers, reports, and other print materials. Documentary evidence is admissible if it's relevant, probative, and authenticated. Common examples of such evidence include:

  • Books
  • Blueprints
  • Photographs
  • Medical records
  • Text messages
  • Computer printouts
  • Written statements

Common law rules only allowed for original documents. But FRE 1003 provides for the admissibility of duplicates. The best evidence rule also allows for copies in the event the original document is unavailable, lost, or destroyed.

For example, emails are electronically stored. If a party wishes to admit this as evidence, they must print out the emails. But suppose a party raises questions about the authenticity of a document. For example, the other side submitted a copy of a lease that only included some of the terms. In that case, the court will request the original document.

Real Evidence

Real evidence refers to tangible physical evidence that a judge or jury can inspect or hold. This type of evidence is commonly depicted on television and in movies. Common examples of real evidence include:

  • Weapons (firearms, knives, sharp objects)
  • Narcotics (marijuana, pills, fentanyl)
  • Fingerprints, footprints, and handprints
  • DNA from clothing and bodily fluids

Even if parties have real evidence, the opposing side can argue that it's circumstantial evidence. Consider finding a suspect's fingerprints in a convenience store after a robbery. An experienced defense attorney could argue the suspect lives in the neighborhood and frequently visits the store. On the other hand, finding a defendant's fingerprints on a murder weapon is highly probative and directly links the defendant to the crime.

Defense attorneys often rely on the exclusionary rule to prevent the admissibility of real evidence. Under this rule, evidence from unreasonable searches or seizures is not admissible. This is because the Fourth Amendment requires the police to have a valid search warrant or probable cause before performing a search.

Testimonial Evidence

When a person takes the stand and answers questions about a case, they provide testimonial evidence. But because people's statements are often tainted by poor memory or bias, several admissibility rules apply.

For example, witnesses may generally only testify about what they observed or perceived during an event. But they may wish to testify about statements they heard outside of court. Such statements are called hearsay evidence and are not admissible as a general rule. They're viewed as less reliable than statements made in court and under oath. There's also no opportunity for cross-examination. But many exceptions to the hearsay rule allow for the admission of statements made outside of court.

Sometimes, a witness may seek to provide testimony about a person's character, often to make the point that the person is the "type" of person who would or wouldn't say or do what's at issue in a case.

Like hearsay, this type of evidence also has reliability problems. It does not directly show whether the person actually did or said something. Because of this, character evidence is generally not admissible. But exceptions exist.

Suppressing Inadmissible Evidence

When one side of a case tries to introduce evidence that isn't relevant, material, or competent, the other side can ask to suppress the evidence on admissibility grounds before or during the trial. One area where a motion to suppress is commonly raised is with chain of custody issues, where a piece of evidence isn't adequately secured from its collection to trial.

So, for example, if one side can show that a blood sample was not properly labeled or a weapon wasn't properly locked and stored in an evidence room, there's no way to trust the results of any subsequent blood test or fingerprint analysis. While this evidence may be relevant and material, it's not competent. There are intervening custody problems that may lead to inaccurate test results.

Talk to an Attorney About the Evidence in Your Case

An experienced criminal defense attorney will challenge the prosecutor's evidence and help discover and present stronger evidence in your favor. So, it's essential to give your attorney as much time as possible on your case. Find an experienced criminal defense lawyer near you if you're charged with a crime.

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