Glass as Evidence Properties The composition of glass is unique and therefore identifiable. 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? Physical vs. Chemical Properties chemical composition (SiO 2 )chemical composition (SiO 2 ) density (Physical)density (Physical) refractive index (Physical )refractive index (Physical ) 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. Forensic Science: Fundamentals & Investigations, Chapter 145 Application of Refractive Index to Forensics Submersion methodused when glass fragments found at the crime scene are small 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 Videoglassevidence.weebly.com/video.htmlhttp://forensics- glassevidence.weebly.com/video.html 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 fragmentBecke 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 Becke Lines What is Glass? Glass is an amorphous solid.Glass is an amorphous solid. Silicas chemical name is silicon dioxideSilicas chemical name is silicon dioxide Would this structure affect HOW glass breaks? Would this structure affect HOW glass breaks? 11 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. What type of glass is this? How is glass used by Forensic Scientist? Glass as evidence By analyzing the fracture patterns:By analyzing the fracture patterns: 1. what object hit the glass1. what object hit the glass 2. from which direction the object came2. from which direction the object came 3. sequence of events 3. sequence of events 4. composition of specialized glass4. composition of specialized glass CLASS or INDIVIDUAL EVIDENCE ? Glass is Class Unless. Glass evidence is considered class evidence, because it is mass-produced However if pieces of broken glass fit Forensic Science: Fundamentals & Investigations, Chapter 1418 First one Stops the Second one What pressure is found on ENTRY and EXIT side of glass? Compression and Tension ROT Radial-----Opposite side----Tension CSC Compression---Same side---Concentric 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 Entry and Exit holes Blunt Object Fractures Heat Fractures 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.