The Law of Evidence

The laws of evidence are lengthy and complicated, and many books have been written on the subject. Therefore, while this overview is thorough enough for most readers, it's also intended as a guide for further research for those who want more.

Types of Evidence

Should you continue your study, you'll find that authors differ in their manner of classifying evidence. Some write that there are three types, while others list four, and still others break evidence down into many more categories.

For the purpose of this book, there are four kinds of evidence: testimonial, real, documentary, and demonstrative evidence. Other types referred to in investigations and in court are usually subtypes of these four — and many of them often overlap:

  1. Testimonial evidence (verbal or written) can be statements, interviews, depositions, and confessions.

  2. Real evidence is anything whose materiality and relevance are obvious, and which is directly involved in a case. Also called physical evidence, it can be a weapon, a wrecked automobile, a bloody shirt, or forensic and trace evidence such as DNA, hairs, and fibers.

  3. Demonstrative evidence is anything that is the representation of an object. It can be photos; x-rays; audio and video recordings; illustrations; maps; computer simulation, animation, and reconstruction; models; and more.

  4. Documentary evidence is anything in the form of documents that is presented in order to examine its contents. It can be records (written, printed, on film, microfiche, etc.) such as wills, contracts, letters, invoices, and printed e-mails. It is subject to authentication, usually by testimony. Documents presented for a different purpose, such as proving that they were handled and contain prints from a victim or suspect, are real evidence, but they may be documentary as well if the contents are relevant.

Read about rules of evidence, which addresses evidence as it relates to that which can be testified to. The rules, however, apply to all evidence. Some of these rules apply to every type of evidence, some only apply to one, and some apply to several types.

Why do I need to know about rules of evidence?

When you are working a case, you should be aware of basic principles of evidence so you can recognize what is usually accepted into the court record and what isn't. Knowing these rules will help ensure that your work is accepted if the case goes to trial.

Putting Evidence Together for Proof

Evidence exists as the means for establishing facts. When enough facts are gathered, they prove a point in question. Standards necessary for proof are different depending on whether the case will be tried in civil or criminal court. In civil court, the standard for proving a point — and the ultimate point of the defendant's guilt — is a preponderance of evidence. In criminal court, the standard is beyond a reasonable doubt. The House Judiciary Committee uses clear and convincing evidence as the standard for proving impeachments.

  • A preponderance of evidence. This is the lowest level of proof of guilt. It relies on jurors concluding that evidence points more toward one direction than another, or that the defendant is more likely guilty than not guilty or vice versa.

  • Beyond a reasonable doubt. This doesn't mean there can be no doubt whatsoever; it means that guilt must be proved beyond a “reasonable” doubt, beyond that standard of doubt that would make a reasonable person hesitate.

  • Clear and convincing evidence. The level of proof required is somewhere between the other two; it must be proved that evidence points substantially more in one direction than the other.

Standards of proof are different from burden of proof, which means the obligation to prove an allegation or allegations. In criminal cases, the prosecution, not the defense, has the burden of proof — the burden to prove charges against the defendant. Investigators use different methods for putting evidence together and proving facts. The scientific method is the one most often used.

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