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Rules of evidence are created to assist in the search for truth and promote a fair process for both parties. This is to ensure that they have both had their day in court by making the best possible presentation to their case. Rules of evidence are the most important in common law criminal justice systems which retain the jury system, since it is thought that these rules safeguard against jury's giving inappropriate weight to certain types of evidence. As the state has far greater resources (i.e. advantage) than the Defense, the Prosecution has a duty to make pre-trial disclosure to even out the playing field. Certain rules of evidence also provide a deterrent effect against prosecutorial or police misconduct, improve efficiency in the administration of justice. Finally, other rules, like rules of privilege, are intended to affect out-of-court behavior. Evidence should be material and relevant.

Some evidence, even if material, relevant, and unprejudicial, may still be inadmissible if it was obtained in an illegal manner.

Types of Evidence


There are various types of evidence that a defense attorney will encounter during a case:

  • Direct evidence is evidence which, if true, proves a relevant fact conclusively. For example, eyewitness testimony is a type of direct evidence. Direct evidence is not necessarily more reliable than any other kind of evidence. See, Eyewitness Misidentification. Direct evidence establishes a material fact without the need for any inferences to be drawn by the trier of fact.
    • If only one fact can be drawn from the evidence, then the jury (trier of fact) will make that conclusion.
    • If more than one fact can be drawn, the judge (trier of law) must determine which inferences are possible.
      • The judge (trier of law) determines the relevance: could the inference be drawn.
      • The jury (trier of fact) determines the weight: should the inference be drawn.
  • Circumstantial evidence is evidence which indirectly, through inference, aids the trier of fact in inferring the existence of a fact in issue. For example, fingerprints or DNA found at the scene would be circumstantial evidence. Circumstantial evidence can be more reliable than direct evidence.

Examples of evidence:

  • There is a "no pets" rule in your apartment building, but you think your neighbor keeps a dog in his apartment. In order to prove this, you want to present the following evidence:
    • Direct testimonial evidence: a witness saying "I saw the dog" - evidence that there was a dog in the apartment, but not necessarily that the dog belonged to your neighbor
    • Direct real evidence: a picture of the dog with your neighbor in the apartment
    • Circumstantial documentary evidence: a dog license in your neighbor's name
    • Circumstantial: dog hair found on your neighbor's sofa
  • Remember that some sorts of evidence could fall into more than one category.
  • Judicial notice is evidence that the court declares is proven through authority or common knowledge. When judicial notice is taken, there is no need to call any evidence: the judicial notice replaces it. Basically, it consists in asking the court to take as truth a particular fact that counsel is proposing. Proof that reference is authoritative is usually required. The rationale for judicial notice is cost and efficiency. Judicial notice has to be relevan to a matter in issue. However judicial notice is a matter of discretion. Courts are more likely to take judicial notice of legislative facts (e.g. when interpreting statutes) than adjudicative facts (i.e. material facts). Courts take more judicial notice of facts in sentencing.

Judicial notice of facts occurs when:

- Common fund of knowledge (e.g.: high-heeled shoes are fashionable but unstable ; cost of child-rearing).

- Local areas have common understanding or common knowledge (e.g.: impaired driving in a community).

- A group of persons have common knowledge (e.g.: picket line = barrier to union members and sympathizers ; cost of child-rearing).

The threshold for judicial notice is strict: a court may properly take judicial notice of facts that are so notorious or generally accepter as not to be the subject of debate among reasonable persons or capable of immediate and accurate demonstration by resort to readily accessible sources of indisputable accuracy (e.g.: dictionaries, scientific treatises or principles ; see Olson v. Olson).

  • Real evidence is some actual physical item involved in the case. For example, the murder weapon is real evidence. This evidence needs to be related directly to the case by testimony and its condition established.
  • Demonstrative evidence is a depiction, prepared for trial, that represents an item involved in the case. Following are some examples of demonstrative evidence: photo of the murder weapon, surveillance camera footage, computer simulations, diagrams, maps, x-rays, videotape, illustrations or any other item specifically created for trial.

A criminal defense attorney may object to real or demonstrative evidence on the following grounds:

  1. No identifying witness
  2. Gaps in chain of custody
  3. Opportunity for tampering or contamination occured
  4. Item is not a true or accurate depiction of what it purports to be.

Evidence Codes


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