3.1: Evidence

• Evidence is critical to a trial, it provides the foundation for the arguments the attorneys plan to offer.

• Evidence can be defined as information— whether in the form of personal testimony, the language of documents, or the production of material objects— that is given in a legal investigation to make a fact or proposition more or less likely.

• In a trial, the jury or judge hears the facts or statements of the case to decide the issues; whoever determines guilt or innocence is called the trier of fact.

3.2: Kinds of Evidence

• Circumstantial evidence –Evidence based on inference and not on personal knowledge or observation.

• Conclusive evidence – Evidence so strong as to overbear any other evidence to the contrary.

• Conflicting evidence – Irreconcilable evidence that comes from different sources.

• Corroborating evidence – Evidence that differs from but strengthens or confirms other evidence.

• Derivative evidence – Evidence that is discovered as a result of illegally obtained evidence and is therefore inadmissible because of the primary taint.

• Exculpatory evidence – Evidence tending to establish a criminal defendant’s innocence.

• Foundational evidence – Evidence that determines the admissibility of other evidence.

• Hearsay – Testimony that is given by a witness who relates not what he or she knows personally, but what others have said, and that is therefore dependent on the credibility of someone other than the witness.

• Incriminating evidence – Evidence tending to establish guilt or from which a fact trier can infer guilt.

• Presumptive evidence –  Evidence deemed true and sufficient unless discredited by other evidence.

• Prima facie evidence – Evidence that will establish a fact or sustain a judgment unless contradictory evidence is produced.

• Probative evidence –  Evidence that tends to prove or disprove a point in an issue.

• Rebuttal evidence – Evidence offered to disprove or contradict the evidence presented by an opposing party.

• Tainted evidence – Evidence that is inadmissible because it was directly or indirectly obtained by illegal means.

3.3: Transfer and Persistence

The conditions that affect transfer amounts include the following:

• The pressure applied during contact;

• The number of contacts (six contacts between two objects should result in more transferred material than one contact);

• How easily the item transfers material (mud transfers more readily than concrete);

• The form of the evidence (solid/particulate, liquid, or gas/aerosol);

• How much of the item is involved in the contact (a square inch should transfer less than a square yard of the same material)?

• Direct Transfer – evidence that is transferred from a source to a location with no intermediaries.

• Indirect Transfer– involves one or more intermediate objects—the evidence transfers from A to B to C.

• Locard Exchange Principle –  states that information is transferred when two things come into contact.

  • Cross transfer -- a Locard's principle, which states that every contact leaves its trace, whether that be someone entering or leaving a scene or someone leaving or picking up evidence.

• Persistence – the second part of the transfer process.

  • Once the evidence transfers, it will remain or persist, in that location until it further transfers (and, potentially, is lost), degrades until it is unusable or unrecognizable, or is collected as evidence.

• Contamination – an undesired transfer of information between items of evidence.

  • It is itself evidence of a kind; that is why it is so difficult to falsify a case or plant evidence.

3.4: Identity, Class, Individualization, and Evidences

• Identification– the examination of the chemical and physical properties of an object and using them to categorize the object as a member of a group.

• Class – a set or category of things having some property or attribute in common and differentiated from others by kind, type, or quality.

• Individualization – categorizing an item in a set or class that has one and only one member.

  • The Assumption of Uniqueness in space is an inherently non-provable situation.

  • Things do not stay the same over time or change at the same rate.

• Questioned Evidence – Evidence that has unknown sources.

• Known Evidence – Evidence that is known where the sample originated.

3.5: Relationship and Context

• The relationships between the people, places, and things involved in crimes are critical to deciding what to examine and how to interpret the results.

• Coincidental Associations– two things that previously have never been in contact with each other have items on them that are analytically indistinguishable at a certain class level.
  

• It is important to establish the context of the crime and those involved early in the investigation. This sets the stage for what evidence is significant, what methods may be most effective for collection or analysis, and what may be safely ignored.

• Evidence collection based on intelligent decision-making, instead of fear of missing something, produces better results in the laboratory and the courts.

3.6: Comparison of Evidence

There are two fundamental processes in the analysis of evidence:

1. Identification

2. Comparison: Done to try establish the source of evidence.

The strength of this association depends on several factors, including the following:

• Kind of evidence;

• Intra- and inter-sample variation;

• Amount of evidence;

• Location of evidence;

• Transfer and cross-transfer;

• Several different kinds of evidence are associated with one or more sources.

3.7: Controls

• Controls – materials whose source is known and which are used for comparison with unknown evidence. These are often used to determine if a chemical test is performed correctly.

  • Positive Control –  It is a material that is expected to give a positive result with the test reagents and serves to show that the test is working properly.

  • Negative Control –  it is expected that the results of the test would come out negative.

    • If a negative control is not used, a false positive may be the result.

• Type I Error – serious errors because they can cause a person to be falsely incriminated in a crime.

• Type II Error – it means that a person may be falsely exonerated from a crime that he or she did commit.

It is better to have someone falsely released than falsely accused. Positive and negative controls are usually easy to obtain and should be used to minimize the chance of errors.

3.8: Analysis of Evidence

• Scientific method– proposing and refining plausible explanations about any unknown situation. It involves asking and answering questions formally and then concluding the answers.

  • Hypothesis – particular questions are tested.

• Once collected, the data will be carefully examined to determine what value they have in proving or disproving the hypothesis; this is the probative value of the data