1. First of the Day….

2. If a red house is made from red bricks, and a blue house is made from blue bricks and a black house is made from black bricks and a pink house is made from pink bricks, what is a green house made of….. ?

5. Chapter 14
Chapter 14 Glass
“There is no den in the wide world to hide a rogue. Commit a crime and the earth is made of glass.”
Ralph Waldo Emerson
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6. Chapter 14
Woman hit, and killed by a car while walking to work. Morning jogger hit by a car that swerved off of the road, jumping the curb. (in these cases the victim often bounces off of the windshield of the car)
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10. Chapter 14
Investigators can use glass fragments found at crime scenes to place a suspect at the scene. Fragments may be found in a suspect’s clothing, embedded in shoes as a result of breaking a window to gain entry to a house, or they may be found on a victim of a hit-and-run accident.
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13. Chapter 14
If an ID is made on the make of car, locating a match is possible, especially if the driver goes to have his/her windshield repaired (maybe even through the insurance company!)
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14. Collection and Packaging of Glass Evidence
Chapter 14
Collection and Packaging of Glass Evidence
Collect and submit all glass pieces
if you believe numerous glass pieces were from the same object (e.g. a window, a bottle, vehicle headlights, etc.) and request the lab to attempt a physical match.
Package glass pieces from different locations into different containers, clearly marking the outside packaging as to the location and description of the evidence.
Label large glass pieces with orienting marks (e.g. up/down, inside/outside) when applicable.
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For example: Large glass pieces may have latent fingerprints present & broken edges of glass may have other trace evidence - such as blood, hair, or snagged fibers
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17. There was blood hair on this windshield, And even an
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There was blood
hair on this
windshield,
And even an
Article of clothing
on this one!
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18. Chapter 14
If the fragments can be pieced together, like pieces of a jigsaw puzzle, evidence can be individualized. Most often, though, glass shatters into many fragments - piecing them together is impossible & must be considered to be class evidence.
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19. How can glass be used as evidence?
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How can glass be used as evidence?
Forensic scientists must use as many physical properties of glass as possible to characterize fragments & link fragments from crime scene to a suspect. By studying the fracture patterns of glass, an investigator can re-create a sequence of events to aid in reconstructing a crime.
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20. Chapter 14
Fragments of glass can be compared to determine if they originated from same source. When a pedestrian is struck by a vehicle, the body may be lifted into the air and onto the windshield of the vehicle. Fragments of glass are often embedded in the victim’s hair and clothing
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21. Chapter 14
Suspects breaking in through glass will usually get fragments of glass on their clothing and on the tool used to break the glass. glass particles (questioned glass) found by examining the clothing can be compared to particles collected from the crime scene (known glass) to determine if they have a common origin.
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22. Chapter 14
Properties of the glass like tint, thickness, UV fluorescence, density, and refractive index, must all be similar for the questioned and known samples to have originated from the same source.
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23. Glass Analysis can be used as evidence in many ways.
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Glass Analysis
can be used as evidence in many ways.
individual glass evidence differs from class evidence.
has the properties of reflection, refraction, and refractive index to classify glass fragments.
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25. Chapter 14
Glass Analysis
is this glass?
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26. Characteristics of Glass
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Characteristics of Glass
Hard, amorphous solid
Usually transparent
Primarily composed of silica with various amounts of elemental oxides
Brittle
Exhibits conchoidal fracture
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bullet
concoidal fracture
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28. Chapter 14
A man is found dead in an abandoned house. Upon examination the medical examiner finds that the man was killed by a single gunshot to the head. Three local teens where observed near the house two days earlier. They are picked up and questioned by police. When pressured, the teens admit to having stolen one of the boys' father's guns. They had taken turns shooting at the windows of an abandoned house.
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29. Chapter 14
The teens admit that John shot the gun first, then Jay and last was Fred. At the scene the investigators find three bullet holes in a window. They analyze the angle of each bullet hole in relation to the victim and find that the bullet which passed through the far right side of the window pane is the one which fatally wounded the man.
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30. Chapter 14
Investigators must determine order of the shots. This will tell them which boy fired the fatal shot and allow the investigators to work out what the charges will be against the shooter. Examination of the fractures in the glass will tell them this.
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31. weapon, angle and order of gunshots through glass?
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weapon, angle and order of gunshots through glass?
Is this even possible?
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32. Chapter 14
Common Types
Soda-lime—used in plate and window glass, glass containers, and electric light bulbs
Soda-lead—fine table ware and art objects
Borosilicate—heat resistant, like Pyrex
Silica—used in chemical ware
Tempered—used in side windows of cars
Laminated—used in the windshield of most cars
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33. Physical Characteristics
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Physical Characteristics
Density—mass divided by volume
Refractive index (RI)—the measure of light bending due to a change in velocity when traveling from one medium to another
Fractures
Color
Thickness
Fluorescence
Markings—striations, dimples, etc
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34. Density Type of Glass Density window 2.46-2.49 headlight 2.47-2.63
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Density
Type of Glass
Density
window
headlight
pyrex
lead glass
porcelain
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35. Determination of Refractive Index
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Determination of Refractive Index
Immersion method: lower fragments into liquids whose refractive index is different.
Match point: when the refractive index of the glass is equal to that of the liquid
Becke line: a halo-like shadow that appears around an object immersed in a liquid. It disappears when the refractive index of the liquid matches the refractive index of the glass fragment (the match point)
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36. Determination of Refractive Index con
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Determination of Refractive Index con
The refractive index of a high boiling liquid, usually a silicone oil, changes with temperature
This occurs in an apparatus called a hot stage which is attached to a microscope. Increasing the temperature allows the disappearance of the Becke line to be observed
At match point, temperature is noted and refractive index of the liquid is read from a calibration chart
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37. Chapter 14
The Becke Line
The Becke line is a “halo” that can be seen on the inside of the glass on the left, indicating that the glass has a higher refractive index than the liquid medium. The Becke line as seen on the right is outside of the glass, indicating just the opposite.
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38. Is the Becke line inside or outside here?
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Is the Becke line inside or outside here?
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39. Refractive Index Liquid RI Glass Water 1.333 Vitreous silica 1.458
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Refractive Index
Liquid RI
Glass
Water
1.333
Vitreous silica
1.458
Olive oil
1.467
Headlight
Glycerin
1.473
Window
Castor oil
1.82
Bottle
Clove oil
1.543
Optical
Bromobenzene
1.560
Quartz
Bromoform
1.597
Lead
Cinnamon oil
1.619
Diamond
2.419
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40. Chapter 14
Fracture Patterns
Radial fracture lines radiate out from the origin of the impact; they begin on the opposite side of the force
Concentric fracture lines are circular lines around the point of impact; they begin on the same side as the force
3R rule—radial cracks form a
right angle on the reverse side
of the force.
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41. Chapter 14
Sequencing
A high velocity projectile always leaves a hole wider at exit side of glass.
Cracks terminate at intersections with others. This can be used to determine the order that the fractures occurred.
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43. Chapter 14
Glass as Evidence
Class characteristics; physical and chemical properties such as refractive index, density, color, chemical composition
Individual characteristics; if the fragments can fit together like pieces of a puzzle, the source can be considered unique
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45. Considerations for Collection
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Considerations for Collection
Consider that fragments within a questioned sample may have multiple origins. If possible, attempt an initial separation based on physical properties.
Consider possibility there may be a physical match to a known sample (a piece of glass to a fractured vehicle headlamp). When an attempt to make a physical match is made at site of collection, collector should take precautions to avoid mixing of known & questioned samples.
Any glass samples collected should be documented, marked (if necessary), packaged, labeled.
—Forensic Science Communications
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47. Chapter 14
Collecting the Sample
Glass sample should consist of largest amount that can be practically collected from each broken object and packaged separately. Sample should be removed from structure (window frame, light assembly). Inside & outside surfaces of known sample should be labeled if a determination of direction of breakage or reconstruction of pane is desired.
When multiple broken glass sources are identified, it is necessary to sample all sources.
A sample should be collected from various locations throughout the broken portion of object in order to be as representative as possible.
Sample should be collected with consideration being given to presence of other types of evidence on that sample (e.g., fibers, blood).
—Forensic Science Communications
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