1. Glass as Evidence

2. Unit Overview Most often the composition of glass is unique and therefore identifiable.Most often the composition of glass is unique and therefore identifiable. In science what type of properties can we test?In science what type of properties can we test?

3. Physical vs. Chemical Properties The forensic scientist can determine distinguishing physical and chemical characteristics.The forensic scientist can determine distinguishing physical and chemical characteristics. Glass can be identified its chemical compostion, density, and also by its refractive index.Glass can be identified its chemical compostion, density, and also by its refractive index.

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

5. Forensic Science: Fundamentals & Investigations, Chapter 145 Application of Refractive Index to Forensics Submersion method—used when glass fragments found at the crime scene are small

6. Forensic Science: Fundamentals & Investigations, Chapter 146 Application of Refractive Index to Forensics Place the glass fragment into different liquids of known refractive indexesPlace 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 indexThe glass fragment will seem to disappear when placed in a liquid of the same refractive index

7. Video http://forensics- glassevidence.weebly.com/video.htmlhttp://forensics- glassevidence.weebly.com/video.html

8. Forensic Science: Fundamentals & Investigations, Chapter 148 Application of Refractive Index to Forensics Becke Line a halo-like effect appearing at the edges of a glass fragment when the reflective index of the glass and liquid are differentBecke Line a halo-like effect appearing at the edges of a glass fragment when the reflective index of the glass and liquid are different – If the line is inside the glass perimeter, the glass index is higher than the index of the liquid – If the line is outside the glass perimeter, the glass index is lower

9. Glass has higher refractive index-note white line inside Glass has lower refractive index-note white line outside Becke Lines

10. What is Glass? Glass is an amorphous solid usually made from silica, calcium oxide, and sodium oxide.Glass is an amorphous solid usually made from silica, calcium oxide, and sodium oxide. Silica’s chemical name is silicon dioxideSilica’s chemical name is silicon dioxide Would this structure affect HOW glass breaks? Would this structure affect HOW glass breaks?

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12. Types of Glass Glass used in vehicle wind shields have been created to not break apart when hit.Glass used in vehicle wind shields have been created to not break apart when hit.

13. What type of glass is this?

14. How is glass used by Forensic Scientist?

15. Glass as evidence By analyzing the fracture patterns, forensic investigators can determine what object hit the glass and from which direction the object came, sequence of events and composition of specialized glassBy analyzing the fracture patterns, forensic investigators can determine what object hit the glass and from which direction the object came, sequence of events and composition of specialized glass

16. CLASS or INDIVIDUAL EVIDENCE ?

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

18. Forensic Science: Fundamentals & Investigations, Chapter 1418 Fracture Patterns in Broken Glass Fracture patterns provide clues about the direction, rate, and sequence of the impactsFracture patterns provide clues about the direction, rate, and sequence of the impacts

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

20. Compression and Tension

21. ROT Radial-----Opposite side----Tension

22. CCS Compression---Concentric---Same side

23. Forensic Science: Fundamentals & Investigations, Chapter 1423 Path of a Bullet Passing through Window Glass The angles at which bullets enter window glass help locate the position of the shooterThe angles at which bullets enter window glass help locate the position of the shooter Bits of the glass can fly backward (backscatter), creating trace evidenceBits of the glass can fly backward (backscatter), creating trace evidence perpendicular to the glass shot from the left shot from the right

25. Entry and Exit holes

26. Blunt Object Fractures

27. Heat Fractures

28. Forensic Science: Fundamentals & Investigations, Chapter 1428 Handling of Crime Scene Glass Samples 1. Identify and photograph any glass samples before moving them. 2. Collect the largest fragments that can be reasonably collected. 3. Identify the outside and inside surface of any glass. 4. If multiple panes are involved, make a diagram. 5. Note trace evidence such as skin, hair, blood, or fibers. 6. Package all materials collected to maintain the chain of custody.