Glass & Soil Analysis

Glass Evidence

Class evidence

Glass evidence is considered trace

evidence

Most common substance submitted for

trace analysis

Valuable because it does not degrade

easily

Characterizing Glass

Type of glass

Density by flotation

Refractive index

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

How does Glass break? Forensic Fracture Analysis

Fractured Glass

70 % of glass

Sprays forward

30 % of the glass

Will spray back on

The shooter

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.

Which one was made first?

B was made first

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!

Justice is served!

The glass told his story!!

Trace evidence doesn’t lie!

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.

Justice is served!

The soil not only told his story, but the sequence of

soil evidence was undeniable!

Trace evidence doesn’t lie!!!