physical evidence bsapp.com. types of analysis comparison comparison visual visual microscopic...

Physical Evidence

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Types of Analysis

Comparison

Visual MicroscopicChemical

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ComparisonMost types of evidence require

a control with which to be compared

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Visual Analysis Evidence utilized through unaided

observation

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Microscopic AnalysisEvidence observed with the

use of some type of microscope

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Chemical AnalysisEvidence

subjected to any type of chemical

procedure

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Types of Evidence

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Documents Hand writtenType or PrintedAuthenticity?

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Glass How broken? (Small hole? Big pieces? Inside or outside?)

Link a suspect to a crime scene

FingerprintsBlood bsapp.com

Soils, Minerals, Wood, and Other Vegetative

Matter. Location Link suspectTrace Evidence

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Fingerprints Mainstay of ForensicsWho is on file?

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Hair

What type?How removed?Match to a personDNA

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Fibers

Link suspect to a location or victim

Origin?bsapp.com

Firearms and Ammunition

Circumstances of discharge

Link to suspectLink to weaponLink to victim

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Powder ResidueGSR TestEvidence of shootingCircumstances of shooting

Type of weapon

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Explosives & Propellants

Link to suspect or victim

Origin

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Tool Marks

Match tool to scars

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Impressions

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Drugs Type of Drug?Strength?Origin?Legal?

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Paint

OriginMatch

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Blood, Semen, Saliva, Organs, & other

Physiological Fluids

OriginDNACondition

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1.What are the four types of analysis?2.Explain what “tool marks” are and how they are used in CSI.

What does a CSI observe with each of the following evidences?

1. Documents 2. Broken glass 3. Vegetative & soil samples4. Hair5. Fiber6. Firearms and ammunition7. Powder residue8. Impressions9. Drug samples10.Body fluid

Glass Fractures

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►A burglar shatters a window. Later, police discover glass fragments embedded in his shoes and jacket. A shooter fires bullets through a window but claims someone inside shot at him first. Cracked, fractured or shattered glass yields crucial clues for investigations of crimes and accidents. Forensic glass analysis uncovers those clues using a variety of scientific processes.

► Forensic analysis of glass fractures reveals clues about projectiles, weapons and direction of force.

Glass ►How broken?►Link a suspect to a crime scene►Fingerprints►Blood

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►Radial cracks look like spokes in a bicycle tire, while concentric cracks resemble ripples in a pond. Add gunpowder residue, and there is no doubt someone fired a gun.

Fractures

Conce

ntri

c

Rad

ial

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Direction of Penetration

►Glass bends in response to a force exerted on its surface. When the limit of its elasticity is reached the glass will fracture.

►A projectile hole is inevitably wider at the exit side.

►Often difficult to determine the size and shape of hole in glass whether it was made by bullet or by some other projectile.

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Stress MarksA projectile hole is inevitably wider at the exit side, and hence its examination is an important factor when determining the direction of impact.

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Direction of

Penetratio

n

Concentric

Radial

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Radials

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• Produced first• Form on side

of glass OPPOSITE to where impact originated.

• Like spider webs that spread outward from the impact hole

Concentric

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• Form SECOND

• Encircle the projectile hole

• Start on the same side as that of the force.

Successive PenetrationsA fracture always terminates

at an existing line of fracture bsapp.com

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► Glass fragments from a crime or accident scene sometimes stick to weapons, tools, automobiles or clothing. Forensic glass examiners compare the density of glass fragments--typically, one sample from a suspect and one from the scene of the accident or crime. If the densities fail to match, police may have enough information to exclude fragments as coming from the crime scene source.

► However, identical densities do not indicate a match, since many types and samples of glass may share the same density. Therefore, forensic glass examiners also analyze the refractive index of both samples. Refractive index measures the ratio of the velocity of light as it passes through a medium versus through a vacuum. A match in refractive index may mean that two glass samples came from the same source, although no glass expert can proclaim that with 100 percent certainty.