CRJ 211 Chapters 2 & 3 01/27/2020
Chapter 2: Understanding the Nature of Physical Evidence
Physical Evidence > Testimonial Evidence
● More of a collaboration between the two
○ Physical evidence to support testimonial
● In order to collect physical evidence, one must recognize it
○ One of the most difficult aspects of being a CSS
● Blood, fingerprints, casings, etc; stand out
Class & Individual Characteristics
● Class characteristics = describe traits or characteristics of evidence that allow the item to
be compared with a group
○ Serve best in eliminating possibilities
○ May include size, color, manufacturing patterns
○ Used for trace, example – glass
○ Used for DNA
● Individual characteristics = allow forensic scientist to compare the item with a specific
object or person
and include or exclude it as having originated from that object or person
○ “Unique” from natural variation, damage, or wear
○ Most common is fingerprint, because no two are the same
○ Also used in footwear
○ End goal of forensics
● Locard’s Principle of Exchange = every contact leaves its trace
○ Locard, French criminalist, said to be the father of modern crime lab
○ Two objects came in contact, one material would transfer to second, and second
to first
○ Underlying theory behind trace evidence examination
○ Whole reason why CSS’s collect “touch DNA”
● Cross-Contamination = caused by inappropriate handling of evidence
○ Big problem with trace & serology
■ Our lab’s biggest problem is DNA Section
○ Book gives example of victim sitting in same chair as suspect
○ Example- detectives and officers bringing bloody victim clothing back to scene
○ Does it happen as often as we think?
Fingerprint Evidence:
● Provides individual characteristics
● Developed as fetus @ 12 weeks
● AFIS – Automated Fingerprint Identification System
○ Catalogues and compares hundreds of thousands of fingerprints
● Taxonomy ridge detail three basic ridge patterns
○ Loops = 65%
○ Whorls = 30%
○ Arches = 5%
● Examination is done by looking at the ridge detail and minutiae present
CRJ 211 Chapters 2 & 3 01/27/2020
○ Minutiae = “the small, precise, or trivial details of something”
● Exist in three forms:
○ Latnet: invisible prints created by normal body secretions
○ Patent: caused by deposit of contaminates (bloody or greasy marks)
○ Plastic: impressions in soft surface such as wax
● Latent is most popular
● Nature of Surface determines which technique to use
○ Porous
○ Nonporous-smooth
○ Nonporous-rough
○ Special
● No accurate way to detect when fingerprints will be deposited
Serology & Biological Evidence:
● Has class & individual characteristics
● Biological evidence includes:
○ Spittle
○ Semen
○ Vaginal Secretions
○ Bone/Tissue
● Before DNA, “wet bench” serology was done
○ A,B,O, etc blood type
○ Offered statistical evidence
● Saliva tested for presence of amylase or starches
● Can distinguish between other bodily fluids
● DNA
○ First reported in 1868
○ Book says structure discovered by Watson & Crick in 1950s
■ However, really discovered by Rosalind Franklin, an xray expert, in early
1950s
■ She died of ovarian cancer before her discovery could be shared with
world
■ Only reason why she did not receive Nobel Prize is because they do not
give posthumous nominations
○ DNA is examined from nucleus
■ Only white blood cells have one
○ Alex Jefferys found mechanism of mapping variable regions of DNA molecule,
allowing for comparison in 1984
■ Used to solve homicides in Narborough, UL
○ Went from 1 in 200 wet benching to 1 in 5 million
○ Coined as “genetic fingerprint”
○ Newer technique called polymerase chain reaction (PCR)
■ Allows testing with smaller samples
■ Allows to duplicate small sample
CRJ 211 Chapters 2 & 3 01/27/2020
■ Enabled concept of ‘touch DNA’
Trace Evidence:
● Trace is usually class, but may prove individualization
● Encountered through hairs, fibers, glass, paints, & soil
● Hairs:
○ Hairs can be distinguished species
■ Human hair, general race as well as hair orientation
● Head, pubic, etc.
○ Hair is usually characteristic, but can contain DNA
● Fibers:
○ First identified by orienting source
■ Natural, synthetic, manufactured
○ 90% transferred hairs/fibers lost in first 8 hours following contact
○ Searching & collecting through tape & vacuum
● Glass:
○ Three basic determinations-
■ Glass types: good for evidence to match if from original source
■ Direction of force: determines radical fractures present in first concentric
ring (in or out)
■ Sequence of force: determines which bullet entered glass first
