24.1: Forensic Science in the Criminal Justice System

The Criminal Investigation Process

When a criminal action begins as a result of activity by the police, prosecutor, or grand jury, the criminal investigation process also begins.

Forensic scientists become involved in this process in a number of ways:

• Response to the crime scene:

  • It is the policy of many law enforcement agencies to have a forensic scientist, or perhaps several, attend crime scenes whenever there is a homicide suspected or in cases where there may be a high profile or otherwise notorious crime committed.

• Analysis of evidence:

  • An ongoing job during a criminal investigation process. Forensic scientists will issue reports on their analyzes which are then evaluated by the prosecutor and criminal investigators.

• Depositions – a proceeding in which testimony is given under oath but not in court or before a judge.

  • The main purpose of the deposition is to preserve testimony for trial, but it may also be used as a discovery tool to gain information about what the opposition knows and what witnesses are prepared to say at trial.

• Court Testimony:

  • The most effective way to impart highly technical and complicated facts and opinions to the judge or jury. Forensic scientists may also testify at preliminary hearings.

    • Forensic scientists are designated as expert witnesses when testifying within the areas of their expertise.

Legal Constraints on the Criminal Investigation Process

• Discovery – a process whereby one side in litigation seeks to gather information about testimony and evidence that is in the hands of the other side.

• Reciprocal discovery – a principle of criminal procedure that requires the defendant to give the prosecution copies of any pretrial statements that a defense witness gave during discovery.

• Search and Seizure

  • The Fourth Amendment of the United States Constitution states:

    • “The right of the people to be secure in their persons, houses, papers, and effects against unreasonable searches and seizures shall not be violated and no warrants shall issue, but upon probable cause, supported by oath or affirmation, and particularly describing the place to be searched and the person or things to be seized.”

• Self-incrimination

  • A portion of the Fifth Amendment of the United States Constitution reads in part:

    • “Nor shall any person be compelled in any criminal case to be a witness against himself.”

  • Due Process Clause – protects people against outrageous government behavior.

Production of Evidence: The Subpoena

• Subpoena – an order issued under the direction of a court commanding the presence of a witness at a specific time and place to give testimony or other evidence.

• Subpoena Duces Tecum – a type of subpoena commands not only the presence of the witness in court but also any documentation or evidence in his or her possession that is material to the case.

24.2: Rules of Evidence

• Rules of Evidence – determine what evidence may be admitted, for what uses, and under what conditions.

• Real Evidence –  is physical and it consists of things that help link a suspect to a crime or explain the circumstances of the incident.

• Demonstrative Evidence – consists of supporting materials such as crime scene photos or sketches.

• Testimonial evidence – the oral recitation of facts and sometimes impressions or opinions by a witness under oath.

• Lay Witnesses –  usually limited to first-hand observations and impressions; they are often called upon to state facts.

• Expert Witnesses – often called upon to state conclusions and opinions based upon their examination of evidence or observation of the crime scene or parties to the crime.

• Chain of Custody – both a process and a document that memorializes the transfer of evidence from the custody of one person to another.

• Admissibility of Evidence – evidence that may be presented before the trier of fact (i.e., the judge or jury) for them to consider in deciding the case.

Rules of Admissibility

• Relevance

  • RELEVANCE = MATERIALITY + PROBATIVENESS

  • If evidence is material, it means that it applies to a matter dealing with the case at hand, and not some other case.

  • Evidence is probative if it tends to make a fact or issue more or less probable than if the evidence were not present.

• Competence – a collection of rules and constraints that evidence must pass muster with in order to be admissible.

  • Prejudice Time Wasting

  • Unreliable

  • Improper procedures

  • Existence of Privileges

  • Constitutional constraints

24.3: Expert Testimony

• When a forensic scientist steps into a courtroom to testify, he or she is, in essence, entering a foreign realm where only some of the rules of science apply.

• The legal arena has its own rules and most, but not all, apply to the scientist as expert and they must abide by the rules; experts, however, have leeway in the courtroom that no other witnesses have.

• Ordinary witnesses may only testify to what they have directly experienced through their five senses. This testimony must be factual in nature and the witness, in nearly all cases, is barred from offering opinions, conjectures, or hypothetical information.

Considerations for Testimony

Preparation

• Prepare yourself.

• Always Tell the Truth

• Prior Statements

• Don’t Discuss the Case with Anyone

About Questions

• Listen To the Question Carefully

• Don’t Volunteer Information

• You Cannot Be Asked Leading Questions on Direct Examinations

• Beware of Compound Questions

About Answers

• Avoid Hearsay Testimony

• Objections

• Reference to Documents

• Don’t Guess

• Don’t Argue With the Questioner

• Never Get Angry

• Beware of Yes or No

• Remain Professional on the Stand at All Times