Forensic Science

1
Forensic Science

• Introduction

2
Key Concepts

• Forensic Science
• Physical Evidence
• Class Characteristic
• Individual Characteristic

3
Forensic Science

• Forensic Science is a young science.
• Its successful implementation by criminal
  investigators has only been done within the past
  100 years.

4
Forensic Science

• Forensic Science is unique because it encompasses
  all three scientific disciplines biology,
  chemistry, and physics.

5
Forensic Science

• One definition of forensic science is the
  application of biochemical and other scientific
  techniques to investigate crime.

6
Forensic Science Careers

• Becoming a Forensic Scientist requires an
  education.
• At minimum, you need a bachelors degree to work
  in the field.
• There are many different fields that are used in
  forensic science.

7
Forensic Science

• After a crime has occurred criminal investigators
  may use scientific techniques or forensic science
  experts to help them identify or interpret
  physical evidence from the crime scene.

8
Forensic Science

• Physical evidence from a crime scene comes in
  many different forms.
• Fingerprints
• Hair
• Blood
• Saliva
• Bullet casings, etc.

9
Why process physical evidence?

• Finding and interpreting physical evidence can
• Prove that a crime has been committed
• Establish the identity of the suspects.
• Exonerate the innocent
• Corroborate the victims testimony
• Lead to a confession from a suspect
• Be more reliable than eyewitness evidence.
• Be expected by judges and juries.

10
Physical Evidence

• Therefore, physical evidence is important to the
  Forensic Scientist as it is used to interpret and
  draw important conclusions about the events
  within a criminal case.

11
Physical Evidence

• In general all forms of evidence have class or
  individual characteristics.

12
Physical Evidence

• Class characteristics are not unique to a
  particular object but place the particular bit of
  evidence into a group of objects.

13
Physical Evidence

• Individual characteristics narrow down the
  evidence to one person or a very small group of
  individuals.

14
Physical Evidence

• The type of handgun with which the victim is shot
  is a class characteristic.
• For example, if the bullet came from a .38
  caliber handgun, every .38 caliber handgun on the
  planet is the possible murder weapon.
• However, finding a suspects fingerprint (an
  individual characteristic) on a .38 caliber
  handgun points the investigation in the direction
  of a single person.

15
Physical Evidence

• Alternatively, blood recovered from a crime scene
  that tests show is type B (a class
  characteristic) could come from any of the tens
  of millions of people who share this blood type.
• If the suspect has type B blood, he or she
  remains a suspect.
• From there, DNA (an individual characteristic)
  from the suspect and DNA from the blood evidence
  are tested to determine conclusively whether they
  match.
• If, however, the suspects blood is type A, he or
  she is excluded.

16
Physical Evidence

• A single piece of class evidence rarely can be
  used to convict someone, but it can be and often
  is used to exonerate someone.
• However, when multiple types of class evidence
  associate one suspect with the crime and crime
  scene, the weight of that evidence can make for a
  stronger case.

17
Physical Evidence

• The most individualizing types of evidence are
  fingerprints and DNA, because they are completely
  unique.
• Impression evidence such as marks left on a fired
  bullet, shoeprints, tire tracks, and tool marks
  may be unique and therefore have individual
  characteristics.

18
Physical Evidence

• The overriding principle in analyzing individual
  characteristics is that no two things are exactly
  alike.
• No two guns mark a bullet the same way.
• No two pieces of glass fracture in the same
  manner.
• No two pairs of shoes or sets of car tires wear
  in exactly the same way.