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Conducting a Systematic Search for Evidence Various Types of Evidence Collecting and Packaging Physical Evidence Steps to a Crime Scene Terms to Know

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Forensics begins at the Crime Scene!

If the investigator cannot recognize physical evidence or cannot preserve it for the laboratory examination then the case could fall through.

CORPUS DELICTI

“Body of the Crime”

• You must prove:• that a crime has occurred• that the person charged with the crime was responsible for the

crime

• Top Reasons for Committing a Crime• Money• Revenge• Sex• Emotion--love, hate, anger

• Source of Evidence• Body• Primary and/or Secondary Crime Scene• Suspect(s)

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What is Physical Evidence?

Any object that can establish that a crime scene has been committed or can provide a link between a crime and its victim or between a crime and its perpetrator.

What is the value of Physical Evidence?

• It can prove that a crime has been committed and set the scene for the investigation.

• It can back up witness or prove it false.• It can link a suspect with a victim or with a crime

scene.• It can determine the identity of people associated

with a crime.• It can allow investigators to reconstruct a crime.

Evidence Characteristics

Class - common to a group of objects or persons; a group of objects that share properties or characteristics (this evidence considered mainly circumstantial)

Individual - can be identified with a particular person or single source.

ABO Blood Typing Blood DNA Typing

Evidence

1. Transient Evidence – temporary, easily changed or lost, usually observed by the first officer at the scene

• Odor - putrefaction, perfume, gasoline, urine, burning, explosives, cigarette or cigar smoke

• Temperature - of room, car hood, coffee, water in a bathtub; cadaver

• Imprints and indentations - footprints; teeth marks in perishable foods; tire marks on certain surfaces

• Markings

Evidence

2. Pattern or Transfer Evidence -produced by direct contact between a person and an object or between two objects. There are several ways of classifying evidence. In this class, we will use:

• Biological• Chemical• Physical• Miscellaneous

Biological Evidence

• Blood• Semen• Saliva• Sweat/Tears• Hair• Bone

• Tissues• Urine• Feces• Animal Material • Insects• Bacterial/Fungal

Chemical Evidence

• Fibers• Glass• Soil• Gunpowder• Metal• Mineral• Narcotics• Drugs

• Paper• Ink• Cosmetics• Paint• Plastic• Lubricants• Fertilizer

Physical (impression)

• Fingerprints• Footprints• Shoe prints• Handwriting• Firearms

• Printing• Number restoration• Tire marks• Tool marks• Typewriting

Miscellaneous

• Laundry marks• Voice analysis• Polygraph

• Photography• Stress evaluation• Psycholinguistic

analysis• Vehicle identification

Evidence

3. Conditional Evidence - produced by a specific event or action; important in crime scene reconstruction and in determining the set of circumstances within a particular event.

• Light--headlight; lighting conditions

• Smoke--color, direction of travel, density, odor

• Fire--color and direction of the flames, speed of spread, temperature and condition of fire

Evidence

Conditional Evidence (cont.)• Location--of injuries or wounds; of bloodstains; of

the victims vehicle; of weapons or cartridge cases; of broken glass, etc.

• Vehicles--doors locked or unlocked, windows opened or closed; radio off or on (station); odometer mileage

• Body--position; types of wounds; rigor, livor and algor mortis

• Scene--condition of furniture, doors and windows; any disturbance or signs of a struggle.

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Steps to a Crime Scene:1. Secure and isolate the crime scene.

Done by the 1st officer on the scene.

2. Lead investigator evaluates the site.

3. Set the boundaries of where the crime occurred.

4. Locate where the perpetrator entered and exited the scene.

5. Conduct a systematic examination of the scene.

6. Record the scene. (photos/sketches/notes)

Crime Scene Team• A group of professionals investigators, each trained in a variety of

special disciplines.• Team Members

• First Police Officer on the scene• Medics (if necessary)• Investigator(s)• Medical Examiner (if necessary)• Photographer and/or Field Evidence Technician• Lab Experts

• pathologist serologist• DNA expert toxicologist• forensic odontologist forensic anthropologist• forensic psychologist forensic entomologist• firearm examiner bomb and arson expert• document and handwriting experts fingerprint expert

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Photographing a Crime Scene

Photos are taken at different angles to get a clear view of the scene. If items/people are removed that should be noted on the photo. Photographs are taken of all the physical evidence that is collected. Digital cameras are the best since you can piece together several

pictures for a 3D view. Video cameras are good for the added bonus of sound records.

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Sketching a Crime Scene Rough Sketch

Draft representation of all the essential information and measurements at a crime scene. Drawn at the scene.

Finished Sketch Precise drawing of a crime scene drawn to scale.

(Drawn with care) Use of computer CAD programs is most common.

19Rough Sketch

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Finished Sketches

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Conducting a Systematic Search for Evidence

Start

Finish

Spiral Search Grid Search

Strip / Line SearchQuadrant / Zone Search

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Conducting a Systematic Search for Evidence After the search is conducted at the scene

more evidence can be collected off of the suspects.

If there is a dead body evidence is looked for on their clothing, fingernail shavings, head/pubic hairs, vaginal/anal/oral swabs, and hand swabs for GSR.

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Collecting and Packaging Evidence Must be done correctly and accurately to

maintain the integrity so that the evidence can prove the case.

Each piece of evidence must be separately collected and packaged

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Collecting and Packaging Evidence

Chain of Custody List of all the people who came

in possession of an item of evidence.

This is very important when establishing validity in a court case.

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Collecting and Packaging Evidence Standard / Reference Sample

Physical Evidence whose origin is known and can be compared to an unknown. Examples:

Soil from a known source vs soil from crime scene. DNA from a suspect vs DNA from crime scene.

Substrate Control Used mainly in arson cases. A piece of unmarked material

is used to compare to the marked material. Example:

A burnt piece of countertop is compared to an non-burnt piece of the table top.

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Terms to Know: Buccal swab

Chain of Custody

Finished Sketch

Rough Sketch

Physical Evidence

Standard/Reference Sample

Substrate Control