glass & soil analysis -...
TRANSCRIPT
Glass Evidence
Class evidence
Glass evidence is considered trace
evidence
Most common substance submitted for
trace analysis
Valuable because it does not degrade
easily
Type of Glass
There are many different types of
glass. This information is used to
determine where the glass evidence
was a part of initially
– Ex: The glass of a light bulb is made
differently and has a slightly different
chemical composition than glass from
eyeglasses
Density by Flotation
Glass is floated in liquid bromoform or bromobenzene
Depending on how the piece of glass floats/sinks in each substance will help determine its density
Once density is known, this is used to find the composition of the glass, helping to determine where the glass is from (a headlight, a window, etc.)
Refractive Index Light bends when it enters a new material.
Knowing this, we can measure how much the
light bends when it enters the piece of glass
evidence. This value is then used to find the
refractive index for that particular piece of glass.
Each type of glass has a specific refractive
index.
– For Example:
Crown Glass (light bulbs) = 1.52
Flint Glass (telescope lens) = 1.65
Radial Fractures
Begin at a point and
radiate outward
from point of impact
-initial crack is on
the side opposite
the applied force Radial
Fractures
Concentric Fractures
Motion of the projectile through the glass puts tension on the front surface of the glass, causing concentric fractures.
-high-speed projectile [a rock] penetrates the glass, it leaves an exit hole larger than it's entrance hole.
-helps to determine the direction on impact.
Concentric
Fractures
A determination of the
direction of force in breaking
a window pane:
-direction of the rib marks
[stress marks on broken edges
of glass that are perpendicular
to one side of glass]
For radial fractures (radiating
from the center):
- the direction of the force is
on the same side as the
tangential parts of the rib
marks.
Projectiles
High velocity – smaller, rounder holes
Low velocity – larger, more irregular holes
Very low velocity - Shatters
Bullets and Glass
It’s possible to
determine the
bullet's direction by
noting the side of
the cone-shaped
hole left by the
bullet.
-small opening is on
the entrance side
Counting Bullet Holes
Determination of the sequence of
bullet holes can be made by noting
the radial fractures.
Radial fractures caused by the
passage of a bullet stop at pre-
existing fracture.
A, B, C
- Radial fractures of B
stop at those of A, C’s
stop at B’s
C, B, A
- Radial fractures of A
stop at those of B, B’s
stop at C’s
The Baltimore Rapist
A serial rapist in
Baltimore broke into a
house where he was
confronted
unexpectedly; the
man panicked and
dove through a
window to get away.
Police eventually
caught him several
blocks away from the
scene.
Samples of glass
slivers were taken
from his clothes and
linked to the broken
window from the
scene for evidence.
But there were other
slivers of glass in his
clothes that did not
match the glass from
the broken window.
Police investigated
other rape scenes in
which the perpetrator
broke a window to get
in and found that the
glass linked this
suspect to three other
rapes!
Soil as Trace Evidence
What is soil?
– Soil is a complex mixture of different
sized mineral grains from the
weathering of rock and organic material.
It is also composed of decay of
vegetation and animals.
– Anything mixed in the soil such as bits
of glass, paint, metal, etc. can be used
in forensic analysis
Properties of Soil
The proportion of sand, silt, clay and
organic matter determines the properties
of the soil:
Sand: Caused by
extreme weathering
Dark organic soil: Caused
by slow decomposition of
vegetative matter
How can soil help catch a suspect?
Example: If a victim was
found near a chain-link
fence, the suspect may
have traces of zinc in the
soil in their shoes.
If a victim was found
outside a home with
asphalt shingles, the dirt
directly below would show
traces of shingle stones
Continued…
If a victim was
found in a yard
with potted plants,
the potting soils
often contain slow-
release mineral
pills.
The Coors Kidnapping Adolph Coors III, chairman of the Coors Brewing company, was kidnapped in the winter of 1960.
Walter Osborne had driven along the dirt road to Coors’s ranch in the Rocky Mountains of Colorado.
While Coors was on his way to work, Osborne forced Coors into his yellow Mercury sedan at a bridge over a creek and fatally wounded him.
Victim:
Adolph Coors III
Suspect:
Joseph Corbett, Jr.
Aka Walter Osborne
Eight days after kidnapping…
Osborne’s burned out
car was found 8 days
later near a municipal
dump on the New
Jersey Shore.
Evidence in the car
led investigators to
Walter Osborne.
Seven months after kidnapping…
Coors’s body was found about seven
months after the kidnapping at another
dump high in the Rockies.
Walter Osborne was also found a couple
of weeks later. But he wasn’t confessing…
Dirt from the undercarriage of the
car:
Soil from the Rocky Mountains
area proves the car was in the
Rockies.
Light gray sand match the soil
In the Coors’s ranch area
Dust that matches the soil at
the dump where the body was
found.
Rounded sand grains that
match the soil found at the
New Jersey dump where the
car was found.