physical evidence + glass evidence

include glass density = mass/volume What type of evidence is considered more reliable – physical or testimonial evidence? Why?

What type of evidence is considered more reliable  – physical  or testimonial evidence? Why?

Physical Evidence

Physical Evidence / why

• Not influenced by human bias or error

• More persuasive to juries.

How is physical evidence useful?  It can…

Show a crime has been committed and sets the scene for investigation

How is physical evidence useful?  It can…

Back up witness testimony or proves it false

How is physical evidence useful?  It can…

Link suspects with to victim(s) and/or crime scene

How is physical evidence useful?  It can…

Help to reconstruct a crime

Types of physical evidence |

Objects

• Weapons, Tools, Firearms, Displaced Furniture, Notes, letters, and papers, Bullets, Vehicles, Cigarette/ Cigar Buds

Types of physical evidence | Body Materials

Blood, Hair, Semen, Tissue, Saliva, Urine, Feces, Vomit

Types of physical evidence | Impressions

Fingerprints, Tire Tracks, Foot Prints, Palm Prints, Tool Marks, Bullet Holes

Identification

Through Identification: The process of determining a substance’s actual chemical or physical identity.

Comparison

Through Comparison: The process of determine whether two or more objects have a common origin.

What is the best (or strongest) physical evidence?

Individual Evidence

Individual Evidence

Evidence that can be linked to a unique, single, specific source.

Individual Evidence | example

fingerprints, handwriting, DNA patterns, and sometimes physical matches, such as a piece of broken glass that fits exactly to another.

What is the most common type of evidence?

Class Evidence

Class Evidence

Evidence that can be linked to a group but not one person

Class Evidence | example

blue jeans, red paint, sandy soil, 2005 Toyota Camry

What can increase the strength of class evidence?

Quantity

Quantity

Having a lot of it! That way the evidence can be used to narrow a list of suspects.

What is Probability?

the frequency of occurrence of an event.

Expected outcome/possible outcomes probability of expected outcome

Probability and forensics | How can it be used?

What percent of the population has those characteristics?

Glass Evidence | importance

found in many types of cases ( breaking & entering ) hit and run

Glass Evidence | importance

can be carried away from crime scene undetected | fragments easily embed in shoes and clothing

Glass Evidence | importance

it is stable and does not declay

what can glass evidence tell about a crime?

it helps reconstruct events in criminal act by indicating

what can glass evidence tell about a crime?

the order of events | by the sequence of the fractures

what can glass evidence tell about a crime?

the direction of the force which caused the fracture | did the break occur from the inside or outside

what can glass evidence tell about a crime?

the type of glass | using physical properties such as density or refractive index measurements

what is glass

an Amorphous solid | irregular pattern of atoms

Amorphous solid

made of silicon dioxide (SIO2) HIGH Melting point over 2,000 (3,632) | Hard & Brittle

Soda-lime Glass ( float glass )

most common & least experience

Soda-lime Glass ( float glass )

window panes and containers

Soda-lime Glass ( float glass )

contains ( soda ) Na2Co3 and ( Lime ) Calcium oxide CaO

Laminated Glass

two sheet of glass with plastic between them

Laminated Glass

used in windshield & skylights

Laminated Glass

inter layer holds it together & prevent from shattering into sharp fragments

Tempered Glass ( Safety Glass )

Similar to soda lime but tougher & shatters into tiny pieces

Tempered Glass ( Safety Glass )

Used in auto side windows high stress area | smaller less damage than big shards

Borasilicate Glass ( Pyrex )

cookware, laboratory, glassware, light bulbs

Borasilicate Glass ( Pyrex )

lime replaced with boron oxide ( B2O3 )

Borasilicate Glass ( Pyrex )

increases resistance to thermal shock ( hot to cold or cold to hot )

Tinted Glass

contains colorants that reduce glare / heat pene

Tinted Glass

decorative use

Lead Glass ( Crystal )

Decorative Glassware, radiation protection

Lead Glass ( Crystal )

lead make softer & easier to mold

Lead Glass ( Crystal )

lime replaced with lead oxide ( PBO ) Dangerous to eat

how can Glass be identified

through density measurements

Density

Mass / Volume

how can Glass be identified.?

through density comparison ( flotation )

density comparison ( flotation )

A glass particle is placed in a liquid whose density is adjusted by adding small amounts of another liquid

density comparison ( flotation )

when the glass piece is suspended, its density

Refractive Index

as light passes from one medium to a different medium it changes speed

Refractive Index

the RI ( refract ) of a material is the ratio of light speed in vacuum to light speed in the material

Refractive Index

RI = c/v material | c = 3×108 m/s ( 186,000 miles, secs )

Refractive Index

different type of glass have different RI’S

Refractive Index identify glass

RI materials = water 1.33 | vegetables oil = 1.47 | Air = 1.00

Window Glass ( soda lime )

1.51

Pyrex

1.47

Tempered ( auto )

1.52

Lead Glass

lead = ( 29% - 55% ) 1.57 - 1.67

individualized

match random stress patterns | match fractures

individualized

since glass is amorphous, no two glass object break the same way

Radial Fractures

lines occur first | produced when opposite side of impact fails

Concentric Fractures

lines form second | produced by the side of impact failing

Direction of Force

small projectiles entry - exit

Entry

smaller holes, smooth surface

Exit

Wider hole, crater shape, rough surface

Radial LInes

shows direction

Radial Fractures

Indicate direction of force

3D rule

radial cracks have right angles on reverse side forces | concentric opposite