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Criminal Investigations


By the end of the lesson, students will be able to:

  • Define criminal investigation.
  • Define the goals of criminal investigation.
  • Define the basic functions of the criminal investigator.
  • Understand how to document a crime scene.
  • Conduct searches for evidence.
  • Gain a basic knowledge of how to obtain information.


Criminal investigation is a complex, sophisticated field. Investigators must be thoroughly familiar with crimes and the elements of each offense. Investigators must know the law and the extent of their legal authority. Investigators must be part psychologist, part scientist, part physic, part philosopher. Investigators must be very objective, not judgmental, and have a strong sense of duty and belief in the “social contract.”

What is the social contract?

What is Criminal Investigation?

Learn more at the Federal Bureau of Investigation Reports & Publications

A criminal investigation is the process of discovering, collecting, preparing, identifying, and presenting evidence to determine what happened and who is responsible. Goals of criminal investigations are to:

  • determine whether a crime has been committed
  • legally obtain information and evidence to identify the responsible person
  • arrest the suspect
  • recover stolen property and
  • present the best possible case to the prosecutor

A successful investigation is one that follows a logical sequence. First, all physical evidence is obtained legally, and all witnesses are effectively interviewed. Then all suspects are legally and effectively interrogated, and all leads are thoroughly developed. Finally, all details of the case are accurately and completely recorded and reported.

Basic Functions of Criminal Investigators

What do criminal investigators do? First and foremost, they provide emergency assistance. They then proceed to secure the crime scene. They photograph, videotape, and sketch the scene; take notes and write reports; search for, obtain, and process physical evidence; obtain information from witnesses and suspects; and identify suspects. Other aspects of their job entail conducting raids, surveillances, stakeouts, and undercover assignments, and testifying in court.

Effective Criminal Investigators

Effective criminal investigators obtain and retain information; apply technical knowledge; and remain open minded, objective, and logical. They are also culturally adroit and skilled in interacting across gender, ethnic, generational, social, and political group lines. They are emotionally well balanced, detached, inquisitive, suspecting, discerning, self-disciplined, and persevering. Additionally, they are physically fit and have good vision, acute hearing, and a high energy level. It also helps if they have a nosey nature!

Criminal Investigators’ Responsibilities

Criminal investigators should arrive at the crime scene as quickly as possible because:

  • The suspect may still be at or near the scene.
  • Injured persons may need emergency care.
  • Witnesses may still be at the crime scene.
  • A dying person may have a confession or other pertinent information to give.
  • Weather conditions may change or destroy evidence.
  • Someone may attempt to alter the crime scene.

Crime Scene Priorities

Although circumstances at the crime scene may dictate the criminal investigator’s priorities, the first priority generally is to handle emergencies: save life, apprehend suspects, and request assistance. The second priority is to secure the scene. The third priority is to investigate.

Learn more at Crime Scene Investigation -

Preliminary Investigations: Basic Considerations

The initial response is usually by a patrol officer assigned to the area where a crime has occurred.

During the preliminary investigation, criminal investigators measure, photograph, videotape, and sketch the scene. They then proceed to search for evidence. If the investigators find physical evidence, they identify, collect, examine, and process it. Victims, witnesses, and suspects are questioned, and statements and observations are recorded in notes. Following are the steps in the investigative process:

  • Determine if a crime has been committed.
  • Verify jurisdiction.
  • Discover all facts and collect physical evidence.
  • Recover stolen property.
  • Identify the perpetrator or perpetrators.
  • Locate and apprehend perpetrators.
  • Aid the prosecution by providing evidence of guilt admissible in court.
  • Testify effectively as a witness in court.

It is not enough to just collect and analyze evidence. Investigators need to apply the logic of reasoning or the methodology of scientific research investigation. They need what can only be called working theories, which are sufficiently flexible to allow for new information while still demonstrating clear patterns of inference or cause and effect.

A hypothesis is an if-then statement that implies a variable level of certainty, as in “if the victim was mutilated, the perpetrator is most likely disturbed.” Steps in the scientific method of investigation include:

  • Identifying the questions and define the key variables.
  • Specifying the simplifying assumptions.
  • Formulating a hypothesis.
  • Testing the hypothesis with data.
  • Retesting the hypothesis with additional data to validate.


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