Forensic Science
Crime Scene Vocabulary
CRIME SCENE: Any physical location in which a crime has occurred or is
suspected of having occurred.
PRIMARY CRIME SCENE: The original location of a crime or accident.
SECONDARY CRIME SCENE: An alternate location where additional evidence
may be found.
SUSPECT: Person thought to be capable of committing a crime.
ACCOMPLICE: Person associated with someone suspected of committing a crime.
ALIBI: Statement of where a suspect was at the time of a crime.
Types of Evidence
Testimonial evidence includes oral or written statements given to police as well as
court testimony by people who witnessed an event.
Physical evidence refers to any material items that would be present at the crime
scene, on the victims, or found in a suspect’s possession.
Trace evidence refers to physical evidence that is found in small but measurable
amounts, such as strands of hair, fibers, or skin cells.
What will evidence collected at a scene do for the investigation?
• May prove that a crime has been committed
• Establish key elements of a crime
• Link a suspect with a crime scene or a victim
• Establish the identity of a victim or suspect
• Corroborate verbal witness testimony
• Exonerate the innocent.
• Give detectives leads to work with in the case
What evidence can be found at a crime scene?
Brainstorm with your group to come up with a list of evidence you
would collect from this crime scene.
Crime Scene Personnel
POLICE OFFICERS are typically the first to arrive at a crime scene. They are
responsible for securing the scene so no evidence is destroyed and detaining
persons of interest in the crime.
SCENES OF CRIME OFFICERS document the crime scene in detail and are
usually skilled photographers trained in lifting finger prints and foot/tire
impressions – usually collect physical evidence for less serious crimes.
THE CRIMINAL IDENTIFICATION OFFICER – searches crime scene; finds,
gathers and analyzes evidence then if needed sends evidence to labs for necessary
analysis
The REGIONAL CORONER (if a homicide) may or may not be present to
determine a preliminary cause of death.
SPECIALISTS (entomologists, forensic scientists, forensic psychologists) may be
called in if the evidence requires expert analysis.
CRIMINAL INVESTIGATIONS BUREAU OFFICER is the detective who
interviews witnesses and consults with the CSI unit. They investigate crimes by
following leads provided by witnesses and physical evidence; they also interrogate
and eventually arrest suspects.
Crime Scene Protocol
Step 1: Interview
The first step in investigating a crime scene is to interview the first officer at the scene or the
victim to determine what allegedly happened, what crime took place, and how the crime
was committed. This information may not be factual information but it will give the
investigators a place to start.
Step 2: Examine
The second step in the investigation of a crime scene, which will help identify possible
evidence, identify the point of entry and point of exit, and outline the general layout of the
crime scene.
Step 3: Document
The third step in the protocol involves creating a photographic record of the scene as well as a
rough crime scene sketch to demonstrate the layout of the crime scene and to identify the
exact position of the deceased victim or other evidence within the crime scene.
Step 4: Process
This is the last step in the protocol. The crime scene technician will process the crime scene
for evidence, both physical and testimonial evidence. It is the crime scene technician’s
responsibility to identify, evaluate and collect physical evidence from the crime scene for
further analysis by a crime laboratory.
Investigating the Evidence
Forensic Science disciplines at many
major Crime Labs include the
following:
Drug Chemistry – Determines the presence of controlled substances and the identification
of marijuana.
Trace Chemistry - Identification and comparison of materials from fires, explosions, paints,
and glass.
Microscopy – Microscopic identification and comparison of evidence, such as hairs, fibers,
woods, soils, building materials, insulation and other materials.
Biology/DNA – Analysis of body fluids and dried stains such as blood, semen, and saliva.
Toxicology – Tests body fluids and tissues to determine the presence of drugs and poisons.
Latent Prints - Identification and comparison of fingerprints or other hidden impressions
from sources like feet, shoes, ears, lips or the tread on vehicle tires.
Ballistics (Firearms) – Study of bullets and ammunition through the comparison of
markings on fired bullets, cartridges, guns, and gunpowder patterns on people and objects.
Toolmarks – Examines marks left by tools on objects at a crime scene or on a victim, such
as a hammer used to break a door or a screwdriver used to pick a lock.
Questioned Documents - Examination of documents to compare handwriting, ink, paper,
writing instruments, printers, and other characteristics that would help to identify its origin.
Chain of Custody
• Testimony and documentation that details the
location and condition of evidence from seizure
to trial.
• It assures the court that items entered into
evidence are in the same condition as when
they were seized.
• The chain of custody and the procedures used
to analyze evidence are more often challenged
than the science behind the analysis.
“FORENSIC”
• FROM LATIN
• “FORENSIS” OR “FORUM”
• In other words, “COURT”
• “Forensic” is an adjective meaning:
“related to court.”
DIRECT
DIRECTEVIDENCE
EVIDENCE
VS.
VS.
CIRCUMSTANTIAL
CIRCUMSTANTIAL
EVIDENCE
EVIDENCE
DIRECT vs
CIRCUMSTANTIAL
• Which is stronger according to the law?
• NEITHER
• “The law treats both equally. Neither is necessarily better
or worse than the other” (Standard Jury Instructions)
• Which is stronger in reality?
• CIRCUMSTANTIAL
• NO DOUBT ABOUT IT
Locard’s Exchange Principle
“Wherever he steps, whatever he touches, whatever he leaves, even
unconsciously, will serve as a silent witness against him. Not only
his fingerprints or his footprints, but his hair, the fibers from his
clothes, the glass he breaks, the tool mark he leaves, the paint he
scratches, the blood or semen he deposits or collects. All of these
and more, bear mute witness against him. This is evidence that
does not forget. It is not confused by the excitement of the moment.
It is not absent because human witnesses are. It is factual evidence.
Physical evidence cannot be wrong, it cannot perjure itself, it cannot
be wholly absent. Only human failure to find it, study and understand
it, can diminish its value.”
– Professor Edmond Locard (1877-1966)
On the Negative Side
Ultimately, forensic analysis is still dependent upon human
interpretation; the results of forensic testing must still be
interpreted by a person and thus can be misinterpreted.
IS DNA
STRONG
EVIDENCE?
ABSOLUTELY
WHAT TYPE
OF EVIDENCE
IS D.N.A.?
CIRCUMSTANTIAL
IS “DIRECT
EVIDENCE”
(EYEWITNESS
EVIDENCE)
STRONG?
In the past, there have been miscarriages of justice, persons
have been wrongly convicted, because eyewitnesses have
made mistakes.
It is quite possible for an honest witness to make a mistake
in identification. Honest people do make mistakes. An
apparently convincing witness can be mistaken. So can a
number of apparently convincing witnesses.
STANDARD
JURY
INSTRUCTIONS
FORENSIC EVIDENCE IS VERY
IMPORTANT
(LIKE ALL CIRCUMSTANTIAL
EVIDENCE)
* PREVENTING MISCARRIAGES OF JUSTICES
* FINDING THE PROPER PERPETRATOR
* EXCLUDING THE INNOCENT
* PROVING THE CASE IN COURT
FORENSIC EVIDENCE’S ROLE IS REALLY TO PROVIDE
NEW AREAS OF CIRCUMSTANTIAL EVIDENCE WHICH:
•CONFIRMS IDENTIFICATION EVIDENCE
- and •CAN PROVE A CASE ON ITS OWN (EVEN WHERE
THERE IS NO DIRECT EVIDENCE)
•WE HAVE ALWAYS HAD
CIRCUMSTANTIAL EVIDENCE
•CIRCUMSTANTIAL EVIDENCE HAS
ALWAYS BEEN HUGE
•FORENSICS HAS SIMPLY BROKEN
WIDE OPEN THE WORLD OF
CIRCUMSTANTIAL EVIDENCE
•THE FORENSIC IDENTIFICATION
SERVICE GIVES US CELL PHONE
RECORDS
• GREAT EVIDENCE
• WHO CALLED WHOM
• AND WHERE THEY WERE
• BUT NOT FORENSIC SCIENCE
THE BOTTOM LINE
•CIRCUMSTANTIAL EVIDENCE IS THE KEY TO MOST
CRIMINAL CASES.
•CIRCUMSTANTIAL EVIDENCE HAS BEEN AROUND
FOREVER.
•FORENSIC EVIDENCE, AT ITS CORE, IS JUST A
POWERFUL NEW ASSORTMENT OF
CIRCUMSTANTIAL EVIDENCE.