Case Study: Susan Nutt (1987)

At 9:30pm on a cloudy, dark night in February, 19-year-old Craig Elliott Kalani went for a walk in his neighborhood in northwest Oregon but never returned home. A hit-and-run driver killed him. Crime-scene investigators collected pieces of glass embedded in Craig’s jacket and other glass fragments found on the ground near his body.

Police searched for a vehicle that had damages consistent with a hit-and-run accident. They found a car with those types of damages that belonged to a woman named Susan Nutt. In order to connect Ms. Nutt and her car with the crime, the police had to match the glass from the crime scene to the glass in her car. The scientists found that windshield glass from the crime scene contained the same 22 chemical elements as those used to make the glass in Ms. Nutter’s car. The scientists considered both samples of glass to be a definite match.

The glass evidence helped convict Susan Nutt of failure to perform the duties of a driver for an injured person. She was sentenced to up to 5 years in and prison and 5 years’ probation

Glass Cartoons

Glass: Opening Questions

• 1. How can glass evidence be useful to forensic science?

• 2. In what types of crimes or situations may glass evidence be extremely valuable?

• 3. What type of evidence do you think glass is: class or individual? Explain why.

• 4. What are some physical or chemical characteristics of glass that could help to distinguish one type of glass from another?

• 5. When glass breaks, what do the fracture patterns look like? Do they vary depending on the type of glass?

GLASS NOTES

What Is Glass?

• Glass is an amorphous solid Lacks a rigid, ordered crystal structure of

materials

• Most common ingredient is quartz sand

• Depending on the type or color of glass that is being made, different metal oxides are added

Amorphous vs. Crystalline StructureAmorphous Structure: Glass Crystalline Structure: Salt (NaCl)

Glass Manufacturing

• It is an automated process– Led to mass production

Mass production means greater uniformity and less ability to discriminate

• Most glass today is called float glass – Made by pouring the molten material onto a

bath of melted tin, resulting in a very smooth surface

How Float Glass is Made

Examples of Float GlassCrystal Palace railway station, London Old window in Jena, Germany

Float glass = in upper left section of window

The remaining sections are possibly not float glass as indicated by the distorted reflections of a tree.

Glass Manufacturing

• Tempered glass – Created by subjecting glass to extreme heat then

cold, repeated over and over, during the manufacturing process

Glass breaks into smaller squares rather than into sharp shards

• Windshields are specialty glasses made by a having a plastic middle layer that is sandwiched between two layers of glass.– The plastic layer helps hold the glass layers together.

Tempered Glass: Shattering Examples

A telephone booth with smashed tempered glass in Holloway, London.

Tempered Glass: Car Front Windshields

Glass In Forensics

• Used in solving automobile accidents, hit-and-runs, burglaries, and assaults

• Glass is a type of transfer evidence– Can be individualized and linked to a common

source Only can individualize a glass fragment, if can

fit it like puzzle piece to its source

Glass In Forensics• Because of a lack of order

and pattern, glass breaks in random patterns

• An impact in glass produces two types of fractures – Radial (radiating out from

the point of impact)

– Concentric (forming circles around the impact)

radial

concentric

Radial and Concentric Glass Fractures

radial

concentric

Direction of Force Direction of force can be determined by looking at

the cross section of the fractures

• The lines created in the glass, called ridges or Wallner lines, show distinctive patterns depending on whether the fractures from which they are collected are concentric or radial

Direction of Force

• Most reliable determinations are from results closest to the original impact

• Perpendicular marks are found on the edge opposite way force was pushing

• Remember: RRadial cracks form RRight angles on the

RReverse side of the force

Direction of Force

Perpendicular marks (~90 degree angles) are found on the edge opposite the way that the force was pushing

Projectile Patterns• Small projectiles passing

through glass at a high velocity will produce characteristic patterns Usually it is a crater with the

largest portion on the face of the glass opposite from the impact

• Exit hole is larger than entry hole

• Lower velocity impacts may not penetrate the glass but leave only a pit or crater on one side of the glass

Shattering Due to Heat• The shattering of glass by heat creates a

distinctive and different fracture pattern characterized by wavy smooth cracks

Order of Impact

• If there are many impacts on the same pane of glass, the sequence of events can be deduced from the fracture patterns Existing fractures from the 1st impact act as

barriers to fractures created by the second impact

– Look for abrupt terminations

Order of Impact Example This photo depicts two bullet holes in safety glass. Which hole was

created first? How can you tell?

1st2nd

The hole on the right was created first. Cracks radiating out from the hole will stop when they encounter another crack. Stress placed on the glass (causing it to crack) will be transferred along the existing crack rather than across it.

Determining Common Source

• Only way to link two fragments of glass to a common source is by the process of physical matching

• Each breakage is unique– Creates pieces of a puzzle that the criminalist must

place the pieces together

Determining Common Source

• The criminalist can obtain other information on the glass characteristics– Color– Thickness– Shape– Texture

Individual Glass Characteristics

The two most common physical parameters used to characterize glass samples are the measurements of density and the refractive index

Density

• Density is mass / volume

Determined by using a floatation technique in which the composition of liquid is varied until the glass sample remain suspended in it

Density

Type of Glass Density

window 2.46-2.49

headlight 2.47-2.63

pyrex 2.23-2.36

lead glass 2.9-5.9

porcelain 2.3-2.5

Question• What happens when you look at a key that is

placed underwater from above water? Why?

Refractive Index

A quantity that measures the bending of light as it travels from one medium into another

• RI = velocity of light in a vacuum

velocity of light in medium

• Always will be greater than 1.00– Water has a refractive index of 1.33 (light travels 1.33

times faster in a vacuum than in water)

Refractive Index

The RI depends on the wavelength of light being used and the temperature of the material

Refractive Index

• Measured using a microscope equipped with a hot stage– Glass is immersed in an oily material with a

known refractive index– Oil is slowly heated

• This changes the refractive index

– When glass is not seen in the oil, it has the same refractive index

Refractive Index

In air

RI = 1.00

In glass

RI = 1.50

Laser

Lower RI to Higher RI = Angle bends toward normal line

Higher to Lower RI = Angle bends away from normal line

Normal line

The Becke Line

The Becke Line is a line that appears as a halo if the refractive indexes of the glass and the material are different The Becke Line will

disappear when the refractive indexes are the same

Becke Lines from Glass

RI of glass (1.525) > RI of medium (1.6) RI of glass (1.525 < RI of medium (1.34)

Becke line on insideBecke line on outside

Refractive Index

Liquid RI Glass RIWater 1.333 Vitreous silica 1.458

Olive oil 1.467 Headlight 1.47-1.49

Glycerin 1.473 Window 1.51-1.52

Castor oil 1.82 Bottle 1.51-1.52

Clove oil 1.543 Optical 1.52-1.53

Bromobenzene 1.560 Quartz 1.544-1.553

Bromoform 1.597 Lead 1.56-1.61

Cinnamon oil 1.619 Diamond 2.419

Glass Videos

• 1. Glass Shattering Montage by Jaime Vendura (4:12)

• 2. Bullet Proof Glass Shooting (0:45)

• 3. Large Fracture Breaking (3:22)

• 4. Smashing Glass (1:58)

• 5. Glass Tables Can Shatter Without Warning (2:26)

• 6. Glass and Its Importance in Early Science (1:35)

• 7. Refraction of Light Causes Rod to Appear Bent (0:09)

• 8. Vanishing Glass Fragment Video (0:27)