FBI Building
Washington, DC
I N T R O D U C T I O N TO F O R E N S I C S C I E N C E
A N D T H E L AW
FORENSIC SCIENCE
 The study and application of science to connect a violation of law to a
specific criminal, criminal act, or behavior and victim
 Includes the business of providing timely, accurate, and thorough information
to all levels of decision makers in our criminal justice system
 Combines Math, Life Science, Technology, Earth Science, Physics, Process
Skills, Social Studies, Chemistry, Language Arts, and others.
 Derived from the Latin forensis meaning forum, a public place where, in
Roman times, senators and others debated, performed, and held judicial
proceedings.
CRIMINALISTICS OR CRIMINOLOGY?
CRIMINALISTICS
CRIMINOLOGY
The scientific examination of
physical evidence for legal
purposes
Includes the psychological
angle: studying the crime
scene for motive, traits, and
behavior that will help to
interpret the evidence
THE LOCARD PRINCIPLE
 Edmond Locard (1877–1966)
 French professor
 Considered the father of criminalistics
 Built the world’s first forensic
laboratory in France in 1910
 Locard Exchange Principle:
 Whenever two objects come into
contact with each other, there is always
a transfer of material.
AT A TRIP TO THE STORE…
What are you in contact with?
What could transfer to you?
What will you leave behind?
How can you prevent transfers?
What could be traced to you?
Other than eyewitnesses, what evidence is there that you were at the
store?
• Is it possible not to leave evidence?
• Could covering your tracks leave evidence as well?
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QUESTIONS, OR
F U N N Y & R E L E VA N T
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BASIC STEPS IN PURSUING JUSTICE:
• Complex and confusing because of different
jurisdictions (federal, state, local); different roles or
procedures, types of crime, etc.
• Criminal Procedures: (Very Basic!!)
– Crime is Committed  Discovered  Suspect
Identified  Police Investigate  Information
Collected  Crime Scene Documented and
Searched  Information Assembled into
Report  Report Given to Prosecutor 
Arrest Warrant Issued
WARRANT FOR
ARREST
• Only possible if the elements of
a crime are present
– If a crime actually occurred
& the accused intended for
crime to happen
– If there is a timely
relationship between a & b
• Suspect must be read Miranda
Rights
OUR RIGHTS & THEIR
EFFECT ON FORENS IC
EVIDENCE
U N D E R S TA N D I N G T H E R I G H T S O F U N I T E D S TAT E S C I T I Z E N S
U N D E R T H E L A W ( B I L L O F R I G H T S ) I S V I TA L W H E N
C O L L E C T I N G , A N A LY Z I N G , A N D P R E S E N T I N G E V I D E N C E I N
THE LEGAL SYSTEM
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THE FOURTH AMENDMENT
• Regulates evidence collection and provides guidelines to search and seizure
– Search Warrant – a judicial order that authorizes the law enforcement
agencies to conduct a search of a location/person and to seize any
evidence of a criminal offense. To issue a search warrant police have to
show the judge that
• There is Probable Cause: Situation in which a reasonable person,
viewing the available information, would conclude that a crime has
been committed and that the suspect committed it
• Evidence or contraband linked to the crime will probably be found on
a certain location on the property or person at issue
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SEARCH WARRANT NOT NEEDED IF…
• Consent is given for the search (no warrant is needed, even in the future,
once consent is given)
• Emergency – someone is in danger, or there might be destruction of evidence
• After an arrest – an officer can search the person and immediate
surroundings
• Plain view – if the police are there legally and evidence is in plain view
• Reasonable suspicion – if police believe they will find a weapon or drugs on a
person or in a car, they can legally search
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THE FOURTH AMENDMENT
– If there is an Unlawful Search and Seizure
• Evidence derived from the search &
seizure will be considered inadmissible
in court, if the case is against the person
whose rights were violated. This includes
an invasion of privacy or a search
without a search warrant and probable
cause
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FIFTH AMENDMENT
• Imposes restrictions on the government's prosecution of persons accused of
crimes. It prohibits self-incrimination and double jeopardy and mandates due
process of law.
– Due Process – everyone is treated the same
– Double Jeopardy
• If a person is found innocent of a crime and more
evidence is discovered after the trial, the person
cannot be put on trial again for that same crime
– Self Incrimination
• Accused can “plead the fifth” and not answer a
question to avoid providing an answer that would
incriminate themselves
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SIXTH AMENDMENT
• Regulates trial policies and gives a right to a speedy trial, impartial
jury, a defense attorney, arraignment, and the right to face witnesses
– Speedy Trial
• Depends on state statute, but generally 90 – 120 days for an
imprisoned defendant, unless waived by the individual.
• Makes it imperative for law enforcement to find all of the
evidence as soon as possible
• Delays lengthen the evidence collection and analysis time
period for law enforcement
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SIXTH AMENDMENT
– Defense Council
• A defendant has the right to an attorney that will defend their
plea. If they can’t afford one, the court must provide one.
– Arraignment: Notification of charges. Occurs within 72 hours of
arrest, and plea is offered
• The more evidence collected before the arrest the better it is
known what to charge the defendant with and where to set
the amount for bail.
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SEVENTH AMENDMENT
• Regulates more trial policies such as having a trial by
peers and a definite & final verdict
– Peers are a random assortment of residents from
the county where the crime was committed.
– All verdicts handed down in the United States
Court are final (unless appealed to a higher court)
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FEDERAL RULES
OF EVIDENCE IN
THE COURTROOM
FEDERAL RULES OF EVIDENCE IN THE
COURTROOM:
• In order for scientific evidence to be
admitted in a court of law, it must be:
– Probative: actually prove
something
– Material: addresses an issue that is
relevant to the particular crime
– Obtained legally
FEDERAL RULES OF EVIDENCE IN THE
COURTROOM:
• Every step of the process for collecting, handling, analyzing,
transporting, and storing evidence is scrutinized in a court of law.
• It is crucial that those in law enforcement understand the types of
evidence, how it is perceived in court, how to testify to its
significance, and the importance of proper evidence collection and
handling to avoid cross-contamination, tampering, and assure
specimen preservation.
EVIDENCE ADMISSIBILITY IN A
COURT
• Not only will the court compare the Bill of Rights to how evidence
was collected, but there are court precedents that determine the
admissibility of scientific results and how those results are
explained in court
– Frye v. United States, 1923
– Daubert v. Dow Pharmaceuticals, 1993
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SCIENTIFIC EVIDENCE STANDARDS
• Frye Standard 1923 Frye v. United States
– Evidence is admissible if methodologies
or scientific principle is accepted by
relevant scientific community
– Evidence is presented and the jury
decides if it can be used
– Offered no guidance on reliability
SCIENTIFIC EVIDENCE STANDARDS
• Daubert Ruling 1993 Daubert v. Dow
Pharmaceuticals
– The judge decides if the evidence can be
entered into trial
– Established rules for admissibility
• If the theory can be tested, peer reviewed,
there is an acceptable rate of error, if the
method has widespread acceptance, and if
the theory follows standards
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THE COU RTROOM
T H E R E A R E F I V E M A I N S TA K E H O L D E R S
I N T H E C O U RT R O O M :
P R O S E C U TO R
DEFENSE
FORENSIC SCIENTIST
JUDGE
POLICE OFFICER/DETECTIVE
ROLE OF THE PROSECUTOR
• Uses evidence & arguments to prove that
the defendant committed the crime
• Presents & defends evidence that supports
their claim
• Subpoenas & questions witnesses, prepares
their case, reviews the case for trial issues,
and discusses plea bargains (sometimes)
ROLE OF THE PROSECUTOR
• Establishes the “MMO” of the suspect:
– Motive—person had a reason to do the crime (not necessary to
prove in a court of law)
– Means—person had the ability
to do the crime
Opportunity—person can be
placed at the crime scene
ROLE OF THE DEFENSE
• Uses evidence & arguments to prove that the
defendant did not commit the crime of which
they are being accused, or support their plea
• Monitors defendant’s rights in pre-trial
process
• Challenges the prosecutor’s evidence
• Subpoenas & questions witnesses, prepares
their case, reviews the case for trial issues, and
discusses plea bargains (sometimes)
POLICE/INVESTIGATOR
• Manages crime scene
• Oversees evidence collection – often done
by officer
• Follows up on leads, questions witnesses
• Makes arrests
• Writes warrants
• Maintains extensive reports and notes
• May assist prosecutor with case preparation
• Prepares for court
FORENSIC SCIENTIST
May collect evidence
Creates/maintains chain of custody
Processes, interprets, and reports on evidence
Follows Constitutional requirements
Often communicates with investigator about
case & prosecutor before trial
• May help prepare posters/materials for court
• Testifies to jury about evidence
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THE EXPERT WITNESS
• Presents & evaluates scientific evidence in court
• Establishes credibility by citing their: educational
degrees, publications, years of experience,
membership in professional societies, &
participation in special courses
• May be subject to cross-examination
• Renders a professional opinion about the
evidence.
JUDGE
• Researches case law
• Reviews motions
• Make decisions on evidentiary
challenges, expert witnesses,
and details of the case such as
crime scene photos being used
• Monitors trial
QUESTIONS, OR
F U N N Y & R E L E VA N T
STORIES TO
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“ R A I S E YO U R H A N D ” I N T E A M S A N D
WA I T TO B E C A L L E D O N TO S H A R E !