Chapter 3: Investigators, the Investigative Process, and the Crime Scene
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Chapter 3
Investigators, the Investigative Process, and the
Crime Scene
Learning Objectives
1. Understand the skills and qualities needed by investigators.
2. Identify the objectives of crime scene investigation.
3. Distinguish between the preliminary and follow-up investigations.
Introduction
While crime rates tend to follow similar patterns across the nation, the response to crime is
typically at the local and state level. However, when criminal justice officials cannot prevent or
deal effectively with crime, other problems are created. First, if individuals commit crime and
escape prosecution, there is no deterrence from committing future illegal acts. Second,
To effectively combat crime, societies need highly effective investigators and trust in the
criminal justice system among the community. These require practitioners to have certain
qualities such as strong ethics, excellent communication skills, initiative, objectivity, an open
mind, and resourcefulness. Furthermore, all cases must be investigated effectively, thoroughly,
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Although rare, there have also been cases of forensic examiners submitting reports on forensic
tests that were never actually performed. In 2016, a New Jersey State Police lab technician
produced a report for a marijuana test that was never conducted, throwing into question the other
7,827 criminal cases on which he worked.
Lecture Notes
I. Types of Offenses
A crime is the commission (doing) of any act that is prohibited or the omission (failing to do) of
any act that is required by the penal code of an organized political state. In most states, a felony
II. The Investigator and the Importance of Investigation
In the search for truth, the most important skill of an investigator is the ability to converse
equally well with a wide range of people, from corporate executives to the homeless.
The investigation of any crime places significant responsibilities on the investigator. These
A. Essential Qualities of the Investigator
Some investigators have a reputation of being lucky, and good fortune sometimes does play a
role in solving a case. Most often, however, the “lucky” investigator is someone with
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excellent training, an open mind, and an eye for detail who, by carefully completing every
appropriate step in an investigation, leaves nothing to chance.
In addition, successful investigators:
• Invariably have a strong degree of self-discipline.
• Use legally approved and ethical methods, ideally derived from scientific research.
• Have wide-ranging contacts across many occupations, including researchers, forensic
scientists, and subject matter experts across a range of fields.
• Are not reluctant to contact experts to help with their investigation.
• Use both inductive and deductive reasoning.
• Know that inductive and deductive reasoning can be distorted-by untenable inferences,
logical fallacies, the failure to consider all alternatives, and bias-and self-monitor
B. Organization of the Investigative Process
The major events in the investigation of crime are depicted in Figure 3-1.
C. The Preliminary Investigation Mindset of Officers Assigned Calls
Although other responsibilities merit great respect, the most important thing officers do is
protect human lives, including their own, and address the situation with an objective and open
mind. On “routine” calls, law enforcement agencies dispatch patrol unit(s) responsive to the
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D. The Preliminary Investigation
The actions taken by the first officer to arrive at the scene of a crime after its detection and
ready for prosecution.
E. 1. Receipt of Information, Initial Response, and Officer Safety Procedures
These include the following steps:
• Note all dispatch and initial information.
o Field notes must be made intermittently throughout the preliminary investigation.
In those notes the condition and placement of people and things at the scene are
recorded.
• Some law enforcement policies give officers the discretion of responding to an
emergency/crime in progress without using flashing lights and/or a siren.
• Do not deviate from going to the call to which you are assigned, except for the most
compelling reasons.
• Approach the scene cautiously, especially when there is thought or known to be a crime
in progress.
• Take time to look, listen, and smell and evaluate what is going on.
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F. 2. Emergency Care
This includes the following steps:
• Remember that saving someone’s life has a higher value than preserving physical
evidence.
• Assess level of injuries and request any needed medical assistance, typically provided
by emergency medical technicians (EMTs).
G. 3. Secure Scene and Control Persons and Evidence
These include the following steps:
• As rapidly as possible, identify the boundaries of the crime scene and secure it.
• In defining the scene, officers must make sure that they also identify possible or actual
lines of approach to, and flight from, the scene and protect them also.
H. 4. Issue a Be-on-the-Lookout
Whenever possible, an APB/ BOLO should include the following points: number of suspects,
age, race, sex, height, weight, build, coloration, birthmarks, hair color and length, condition of
teeth, mustaches and beards, names and/or nick-names, clothing, hats, scars, marks, tattoos,
jewelry worn, deformities (for example, missing finger), any prosthesis, and accent, as well as
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I. 5. Conduct Neighborhood and Vehicle Canvass
A neighborhood canvass is an attempt to locate witnesses who may have heard, seen, or
J. 6. Administrative Procedures for Processing Crime Scenes
The following are the administrative procedures for crime scene processing:
• In smaller departments (such as those with 20 or fewer sworn personnel), the
responding officer may serve as the crime scene technician, and must recognize and
identify physical evidence, document its location through sketching and photographs,
collect it and mark it, package it, and take it to the station for storage where a written
K. 7. The Incident/Offense Report
The officer assigned to the call must prepare an incident/offense report on his or her part in
the investigation.
III. Types of Crime Scenes
The fundamental assumption on which crime scene searches are carried out is Locard’s
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exchange principle: which can be simplified to there is something to be found.
Crime scenes vary in regard to the amount of physical evidence that is ordinarily expected to be
People need additional ways to think about what a crime scene is.
• Criminal incidents may have more than one crime scene.
• On the basis of size, there are macroscopic and microscopic scenes.
o A macroscopic scene is the “large view.” It includes such things as the relevant
location(s), the victim’s and the suspect’s bodies, cars, and buildings.
IV. Organization of the Crime Scene Investigation
The work at the scene is divided into three major functions: (1) overall coordination of the scene,
(2) forensic services, and (3) investigative services.
A. Overall Coordination
The lead investigator assigned to a case usually has overall responsibility for what happens at
a crime scene. In order to fulfill this responsibility he/she must conduct a visual inspection,
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B. Forensic Services
Forensic services is the responsibility of the senior representative of the department’s central
crime laboratory or a crime scene processing unit. He/she may arrive to process the scene
C. Investigative Services
Investigative services include: (1) interviewing witnesses, (2) conducting and documenting
V. Types of Evidence
There are three broad categories of evidence in which investigators have a particular interest: (1)
corpus delicti, (2) associative, and (3) tracing.
A. Corpus Delicti Evidence
Each criminal offense contains a distinct set of elements whose commission or omission must
B. Associative Evidence
Associative evidence is bidirectional in that it connects the perpetrator to the scene or victim
or connects the scene or victim to the suspect.
C. Tracing Evidence
The identification and location of the suspect are the goals of tracing evidence; corpus delicti
and associative evidence may also serve these purposes.
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VI. Typical Crime Scene Problems
Although the procedures to be followed at a crime scene investigation may be neatly delineated
in theory, any number of conditions may render their accomplishment far less feasible than the
VII. Rules for the Crime Scene Investigator
A. Maintain Control
Without control, a life might be lost, evidence destroyed, assignments overlooked, or the
investigation conducted in a generally haphazard manner. How the police relate to the news
When determining information to release to the public during a criminal investigation, many
police departments have explicit policies that outline what may not be released without the
prior approval of the chief executive or a designee and information that may routinely be
released by the PIO, unless there is some unusual situation. Some examples of impermissible
releases include the following:
• The identity of a suspect prior to arrest unless it would aid in apprehending the suspect
or serve to warn the public of potential danger.
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Some examples of permissible releases include the following:
• Age, name, and marital status of an adult accused of a crime.
B. Conceptualize Events
Assumptions that are made must be checked for accuracy as quickly as possible. The failure
to do so may result in an offender’s escaping prosecution and in embarrassment for the
investigator and the department. It may also produce confusion in, or misdirect, the
investigation.
C. Proceed with Caution
In approaching the point of focus, small but extremely important evidence may be altered or
D. Apply Inclusiveness
The rule of inclusiveness dictates that every available piece of evidence be obtained and,
Elimination prints are useful in determining whether a latent fingerprint found at a crime
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scene belongs to the suspect.
E. Maintain Documentation
Documentation of the crime scene is a constant activity, starting with the shorthand record
created by field notes. Other types of documentation that need to be maintained include:
• The crime scene entry log.
• The administrative log, which is the responsibility of the crime scene coordinator and
• The rough sketch of the crime scene; the data used to prepare the finished or final
diagram, which may be drawn by hand or by computer.
• The evidence recovery log, which lists each item of evidence; the names of the
VIII. Infectious Disease Risks and Precautions for Investigators
Investigators are at risk of exposure to infectious pathogens (disease-causing agents), such as
HIV, Hepatitis A, B, and C, tuberculosis, and now COVID-19. Officers should know their
department’s applicable policies, maintain their PPE, use it as needed, and take other appropriate
precautions.
A. HIV/Aids
The human immunodeficiency virus (HIV) is a pathogen that is present in the body fluids of
a person with HIV, such as blood, semen, and vaginal secretions. While the risk of being
infected by HIV among law enforcement is low, danger arises when officers are making
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B. Hepatitis A, B, and C
Hepatitis means inflammation of the liver. In the United States, the most common variants are
hepatitis A, B, and C. HAV is a highly contagious viral liver disease that causes mild to
severe symptoms lasting a few weeks to several months. HBV is the most common serious
C. Tuberculosis (TB)
About one-third of the world’s population is infected with TB. Globally in 2018, 1.5 million
people died of TB, making it one of the world’s deadliest diseases. TB is a chronic bacterial
infection that is spread by air.
D. Coronavirus Disease 2019 (Covid-19)
COVID-19 is caused by a coronavirus called SARS-CoV-2 and is the disease that caused the
global pandemic that upended the world beginning in 2019. Symptoms of COVID-19 include
fever or chills, cough, shortness of breath or difficulty breathing, loss of taste or smell, sore
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E. The Americans with Disabilities Act
Investigators who contract the infectious diseases discussed previously may be covered by the
federal Americans with Disabilities Act (ADA). Under this act, it is illegal to discriminate
IX. The Crime Scene Search
The purpose of the crime scene search is to obtain physical evidence useful in establishing that
an offense has been committed, identify the method of operation, reduce the number of suspects,
and provide leads or evidence of who the perpetrator was.
A. Boundary Determination
In terms of the boundary of the crime scene, it is useful to think of an inner perimeter and an
B. Choice of Search Patterns
There are five basic crime scene search patterns from which the crime scene coordinator
may choose:
• The spiral, depicted in Figure 3-28(a), is usually employed in outdoor scenes and is
normally executed by a single person.
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C. Instruction of Personnel
Even when the same type of criminal offense has been committed, the variation among crime
scenes may be enormous, for example, the murder weapon may be recovered at the scene or
D. Coordination
One of the most important responsibilities of the person in charge of the crime scene is
X. Suspended Searches, Debriefing, and Release of the Scene
Occasionally, it may be necessary to suspend an operation temporarily. In one of the most
common situations, a priority crime with evidence subject to decay requires the temporary
diversion of personnel from another scene where delayed processing will not result in any loss of
physical evidence.
XI. Collection and Care of Evidence
The location of physical evidence during the crime scene search merely marks the first step in its
long journey toward presentation in court. To satisfy legal requirements related to its
introduction in a judicial proceeding, investigators must be able to:
• Identify the evidence and who found it where.
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XII. Visual Documentation of the Crime Scene
Occasionally, the value of an otherwise excellent investigation is reduced by improper or
inadequate visual documentation of the scene.
A. Digital Still Photography
Photographs are taken in such a manner as to provide clear, undistorted high-quality images
that document the condition of the crime scene, evidence, and persons related to a criminal
investigation.
Some of the objectives of still photography are to:
• Record the condition of the scene before alterations occur.
• Record the location of the scene.
There are four categories of still photographs that are often taken, commonly in the following
sequence:
• Orientation
B. Digital Videography
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Using digital videography to document the crime scene offers several advantages. Such
cameras are relatively inexpensive, they incorporate audio, their use can be quickly learned,
and the motion holds the attention of viewers.
C. Crime Scene Sketching and Forensic Mapping
A crime scene sketch is a basic diagram of the scene showing important points, such as the
locations where various pieces of physical evidence were located. Sketches made by hand in
D. Types of Sketching and Methods of Forensic Mapping
Beyond the basic distinction between rough and smooth sketches, there are four basic types of
Because of technological advances over the past 15 years, rapid, automated, and extremely
accurate measurements of crime and traffic accidents scenes have become possible. The
fusion of laser scanning and panoramic cameras has produced extraordinary capabilities
and advantages:
• The systems can easily be deployed; setup time can be as little as 10 minutes.
• Scenes can be documented very rapidly and more thoroughly.
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studied later.
Training for use of the DeltaSphere is conducted over a three-day period. The first half-day is
devoted to setting up and using the equipment, that is, capturing the data, and the remaining
XIII. Submission of Evidence to the Crime Laboratory
A. FBI Forensic Services: Case Acceptance Policy
The successful investigation and prosecution of crimes generally require the collection,
preservation, and forensic analysis of evidence. Evidence submitted to a crime laboratory is
XIV. Investigative Success
Law enforcement will close a case and consider their investigation an administrative success if it
is:
• Cleared by exceptional means, meaning that the offender has been identified; enough
evidence has been gathered to support an arrest, make a charge, and turn the offender over