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What Are the Rules of Evidence?

Popular shows like "CSI" and its spinoffs have made physical evidence seem almost magical. Real trials like the O.J. Simpson trial in 1995 brought DNA evidence and blood spatter evidence into public knowledge. In truth, the rules of evidence remain unclear. What is evidence? Are there federal rules of evidence? Who decides what evidence is admissible and what isn't? How is evidence gathered and entered into trial?

The rules of evidence are an entire law school class by themselves. This article summarizes the basic rules of evidence and some types of evidence admitted into court.

Definition of Evidence

For legal purposes, evidence is an "item or information offered to make the existence of a fact more or less probable." In a criminal trial, it is proof that the crime occurred. In a civil case, it may be proof of a financial transaction.

There are two types of admissible evidence: direct evidence and circumstantial evidence.

  • Direct evidence is based on personal knowledge. When a witness testifies in court to something they saw, heard, or felt, that is direct evidence.
  • Circumstantial evidence is everything else. Physical evidence, DNA, expert testimony, documentary evidence, and video recordings are all considered circumstantial evidence.

There is a misconception about circumstantial evidence that leads some people to believe it is less trustworthy than other evidence. In fact, all evidence except direct witness testimony is circumstantial evidence. Attorneys make inferences between pieces of admissible evidence to establish a chain of causation.

Collecting Evidence

Collecting evidence from a crime scene or a person requires a warrant. The Fourth Amendment to the Constitution states that warrants must "specifically describe the place to be searched and the things or persons to be seized." In Mapp v. Ohio (1961), the Supreme Court ruled that courts must exclude any evidence seized in violation of the Fourth Amendment.

The Exclusionary Rule or "fruit of the poisonous tree" doctrine makes any warrantless search unconstitutional. Courts will rule evidence found in a warrantless search as inadmissible. There are several exceptions to this strict doctrine.

  • Exigent circumstances doctrine: Situations where immediate action is needed to "prevent physical harm to the officers or other persons, the destruction of relevant evidence, the escape of the suspect, or some other consequence improperly frustrating legitimate law enforcement efforts"; Brigham City, Utah v. Stuart547 U.S. 398, 126 S.Ct. 1943, 164 L.Ed. 2d 650 (2006)
  • Inevitable discovery doctrine: When evidence would have been found by other legal means, the lack of a warrant does not invalidate the evidence; Nix v. Williams467 U.S. 431, 104 S. Ct. 2501, 81 L. Ed. 2d 377 (1984)
  • Good faith exception: If officers believe they are acting in good faith, flaws in the search warrant will not invalidate the evidence later; U.S. v. Leon468 U.S. 897, 104 S. Ct. 3405, 82 L. Ed. 2d 677 (1984)

The judge can rule that any item of evidence with breaks in the chain of evidence is not admissible. The chain is created when the evidence is collected from a crime scene or a person (saliva, blood, DNA, etc.). If there is a break in the chain, the defendant can argue that the item of evidence is tainted in some way and, therefore, unreliable.

Admitting Evidence

The Federal Rules of Evidence (FRE) provides general provisions for admitting evidence into federal court. State laws model their own rules of admissible evidence on the FRE. There are also federal rules for criminal procedure and civil procedure. The criminal and civil procedure rules focus on procedural matters in trial court.

Evidence law establishes relevance. A trial judge's job in admitting evidence is determining what evidence to admit and/or exclude. Rule 401 of the FRE explains that evidence is relevant if:

  • It tends to make a fact more or less probable than if the evidence were not admitted; and
  • The fact is of consequence in determining the action.

In other words, evidence must prove or disprove something important to the case to be considered admissible. Otherwise, there is no point in entering it. The judge must balance the desire to enter evidence with the convenience and time available to the court.


The opposing party must receive all items of evidence during the discovery process. This happens near the beginning of the proceedings. In a criminal trial, the prosecution must give all evidence to the other parties, including exculpatory or Brady evidence. Failure to present exculpatory evidence may be grounds for a mistrial.

Inadmissible Evidence

The Federal Uses of Evidence grants judges considerable leeway on the admissibility of evidence. Rule 403 allows a judge to exclude evidence which:

  • Is irrelevant to the case.
  • Has no probative value.
  • Would tend to confuse or mislead the jury.
  • Is unfairly prejudicial to the defendant.
  • Is needlessly cumulative in nature.
  • Would be a waste of time and resources.

For instance, judges often refuse to let prosecutors show gruesome photos of serial killers' death chambers in a criminal case because they would unfairly inflame the jurors. In white-collar crimes, judges may limit the amount of accounting testimony because of the danger of confusing the jury.


There is possibly no legal term as misunderstood or misused as hearsay. Hearsay is not what most people think. The rule against hearsay is so complicated that almost all of the Federal Rules of Evidence is focused on hearsay and its exceptions.

Hearsay itself is simple enough. It is a statement made out of court by someone other than the person repeating it and offered in court as proof of the fact in the statement. For example, Bob is under oath. The prosecutor wants to prove it was raining. Bob testifies, "Jane said it rained." That is hearsay because Jane said it out of court, and Bob is repeating it in court to prove it was raining.

Hearsay is not admissible in court as proof of the thing asserted because the speaker is not there to verify their statement. The Sixth Amendment right to cross-examination means a witness must give their own testimony about things they have personal knowledge about.

Hearsay exceptions

An attorney can get almost any statement through via hearsay exceptions. Most exceptions originally came from common law and are now part of the Federal Rules of Evidence. Rule 803 contains exceptions if the declarant is still available; Rule 804 exceptions apply only if the declarant is unavailable. Rule 801 contains additional exceptions. Some of the most common exceptions include:

  • Present sense impression: The declarant was describing something while experiencing it
  • Excited utterance: An utterance related to a startling event, made while the declarant was still under the stress of the event
  • Recorded recollection: A recording made while the witness's memory was still fresh but which they cannot fully recall
  • Former testimony: If the witness is unavailable, previous testimony given under oath may be read into the record
  • Statement made under belief of imminent death: In some states, the declarant must have died
  • Statement against interest: A statement that a reasonable person would have made only if they believed it was true because it is so contrary to the declarant's interests. Corroborating evidence must support a statement against interest

Depending on how the state classes or interprets the Federal Rules of Evidence, there may be over 27 hearsay exceptions. Many have to do with documentary evidence.

Documents may involve a concept called "double hearsay," in which both the document and the presentation may be hearsay. For instance, a business might need to present documents to show proof of transactions. There is a document exception for hearsay if the business can show trustworthiness in the record-keeping and the person presenting the documents is normally charged with maintaining the records.

Miranda Rights and Hearsay

You may have heard that if police fail to read your Miranda rights, they can't use what you say in court. This is not entirely true. The prosecutor can use your statements for impeachment purposes. Impeaching a witness means showing a witness or defendant tends to be untruthful. The prosecutor can use statements made during your arrest and those made after you received your Miranda rights to show you have a propensity to lie.

Impeachment of a witness is one of the few instances where an attorney, on direct examination of a witness, may use leading questions to get an answer. It can be difficult to rehabilitate a witness after this type of direct examination. Attorney-client privilege could protect a defendant in some cases if the witness's testimony was made in the presence of their lawyer.

Other Types of Evidence

Court rules determine the admission of other evidence. The attorneys request permission to present evidence, and the judge determines its applicability. Not all trials require all types of evidence.

  • Character evidence is witness testimony about a defendant's or other witness's character. It may establish a character for truthfulness or untruthfulness. Character evidence is not used to prove an individual has a tendency to commit a particular crime.
  • Expert testimony is evidence provided by an expert witness. If a trial has technical evidence, like DNA or computer forensics, an expert needs to explain the details in layperson's terms to the jury.
  • Judicial notice is a request by an attorney for the judge to acknowledge a fact that everyone knows is true. This saves the attorneys the time of having to present evidence of it in court.
  • Self-authenticating documents are documents with presumptions of authenticity. Certified copies of public records are examples of self-authenticating documents. Duplicates cannot be self-authenticating.
  • Opinion testimony comes from two sources. Lay witnesses may give opinions based on their observations, such as "How fast do you think the car was going?" Expert opinion may reflect the specific case and the expert's qualifications. State laws vary on the admission of expert opinion testimony.

A trial's purpose is to determine the ultimate issue of guilt or innocence. Evidence is the material used to help resolve that issue. Without real evidence, a jury could not issue a true verdict and judges could only rely on opinion and belief.

Still Have Questions About Evidence? Contact Professional Help

Facing a trial can be daunting and intimidating. The rules about evidence are confusing, and rather than making a mistake it might be a good idea to consult with a legal expert well-versed with what you're going through. Whether you require a criminal defense lawyer, someone to help you with an injury you've suffered, or assistance in a different legal field, meeting with an attorney to discuss your case is an excellent option.


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