1. Glass as Evidence

2. Properties
The composition of glass is unique and therefore identifiable.
What are some CLASS characteristic of glass
ANS: chemical and physical properties
Examples: density, melting point, boiling point, refractive index, etc.
Bertino, Forensic Science Fundamentals of Investigation, pp.394 2

3. Physical vs. Chemical Properties
chemical composition (SiO2)
density (Physical)
refractive index (Physical)
Bertino, Forensic Science Fundamentals of Investigation, pp.394 3

4. Physical vs. Chemical Properties
The bending of light waves because of a change in velocity is called refraction.

5. How to find the Refractive Index
Submersion method—used when glass fragments found at the crime scene are small
Forensic Science: Fundamentals & Investigations, Chapter 14 5

6. Refractive Index
Place the glass fragment into different liquids of known refractive indexes
The glass fragment will seem to disappear when placed in a liquid of the same refractive index
Forensic Science: Fundamentals & Investigations, Chapter 14 6

7. Video

8. Becke Line a halo-like effect appearing at the edges of a glass fragment
Glass has higher refractive index-note white line inside
Glass has lower refractive index-note white line outside

9. What is Glass? Glass is an amorphous solid.
Silica’s chemical name is silicon dioxide
Would this structure affect HOW glass breaks?

10. 10

11. Types of Glass Safety Glass
Bertino, Forensic Science Fundamentals of Investigation, pp.394 11

12. What type of glass is this?

13. How is glass used by Forensic Scientist?
Bertino, Forensic Science Fundamentals of Investigation, pp.394 13

14. Glass as evidence By analyzing the fracture patterns:
1. what object hit the glass
2. from which direction the object came
3. sequence of events
4. composition of specialized glass

15. CLASS or INDIVIDUAL EVIDENCE ?

16. Glass is Class Unless….
Glass evidence is considered class evidence, because it is mass-produced
However if pieces of broken glass fit…

17. Slo mo glass

18. What pressure is found on ENTRY and EXIT side of glass?

19. Compression and Tension

20. ROT
Radial-----Opposite side----Tension

21. CSC
Compression---Same side---Concentric

22. Primary Stops Secondary
Forensic Science: Fundamentals & Investigations, Chapter 14 22

23. Path of a Bullet Passing through Window Glass
perpendicular to the glass
shot from the right
shot from the left
The angles at which bullets enter window glass help locate the position of the shooter
Bits of the glass can fly backward (backscatter), creating trace evidence
Forensic Science: Fundamentals & Investigations, Chapter 14 23

25. Entry and Exit holes

26. Handling of Crime Scene Glass Samples
Photograph glass samples before moving them.
Collect the largest fragments
Identify the outside and inside surface of any glass.
Sketch.
Note trace evidence such as skin, hair, blood, or fibers.
Package all materials collected to maintain the chain of custody.
Forensic Science: Fundamentals & Investigations, Chapter 14 26

27.
Forensic files-shattered dreams