Forensic Science Criminalistics - PowerPoint Presentation

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Forensic Science

CriminalisticsChapter 2The Crime Scene

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Physical Evidence

Any and all objects that can establish that a crime has been committed or can provide a link between a crime and its’ victim or a crime and its’ perpetrator

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The Value of Physical Evidence

Physical Evidence is only valuable when collection is performed with

selectivity

that is determined by the collector’s knowledge of the capabilities of the crime lab

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Forensic Science begins at the Crime Scene

Physical evidence must be recognized and properly preserved for lab examination or it is useless to investigators and/or prosecutors in a court of law

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Securing and Isolating a Crime Scene

Duties of the Arriving Officer:Get medical attention for suspect or victimArrest perpetrator if remaining on premisesSecure the Crime Scene

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Securing and Isolating a Crime Scene

The Arriving Officer

must

prevent unauthorized or unneeded access:

Unnecessary police officers

Neighbors/Onlookers

Members of the Media

Every individual entering a crime scene can potentially destroy important evidence

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Once the crime scene has been secured, a Lead Investigator begins the process of evaluating the immediate area as well as adjacent areas to the crime scene.

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Evaluate the Crime Scene

The Lead Investigator will:

Determine the boundaries of the scene

Document and photograph obvious evidence

Develop a strategy for a systematic examination and documentation of entire scene

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Record the Crime Scene

Accurate records are important for investigators and prosecutors

Useful in subsequent investigations

Document the exact condition of crime scene

Mark exact location of physical evidence

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Methods of Crime Scene Recording

Photography & Videography

May be limited by budget/personnel

Detailed Sketches with accurate measurements

Detailed Notetaking with descriptions of evidence collected

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Crime Scene Photography

The crime scene must be unaltered and in the original state found by investigators

Must be photographed from all necessary angles

Evidence must not be moved prior to photography: if it has been moved, it cannot be reintroduced into the scene for photo purposes

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Crime Scene Photography

Photos must be taken of the entire room and all rooms adjacent to initial crime scene

Close-up photos and panoramic photos are taken and sometimes include a ruler for scale

All pieces of physical evidence are photographed

prior to

removal

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Crime Scene Videography

Increasingly popular due

to affordable

cost

Long-shots and close-ups are taken of scene

Narrations are often included as a method of note-taking

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Crime Scene Sketching

Rough Sketch:An accurate depiction of dimensions of the scene, showing the location of all objects that may have implications to the crime. Done at the scene and used for finished sketch later

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Rough Sketches

Objects are depicted from

two fixed

locations at the scene

Accurate measurements

must be

taken with a tape measure

Sketch evidence by using letters or numbers and a legend at the bottom

Sketch

should always

depict the NORTH direction

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Finished Sketch

A precise depiction of the crime scene, drawn to scaleSometimes drawn with the aid of a computer CAD: Computer-aided drafting

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Notetaking at a Crime Scene

Constant activity at a crime scene that includes the following:

A written description of the scene in a narrative format

Location of physical evidence items recovered

Time evidence discovered and by whom

The condition of the evidence recovered

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Notetaking at a Crime Scene

Tape Recording may also be used to record a crime scene

Videotaping a scene with narration may also be used

All tape/video recordings must be transcribed onto paper for recordkeeping

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Search for Evidence

Must be thorough and systematic

How the search is carried out depends on the location and size of the area and the actions of the suspect(s) and victim(s)

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Typical types of Crime-Scene Searches

Spiral Search Method: Begins from one point of the crime scene and continues in a spiral fashion to another point

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Typical types of Crime-Scene Searches

Strip or Line Search: Several investigators begin side-by-side and search in a straight line and turn around and continue back on an adjacent part of the area

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Typical types of Crime-Scene Searches

Grid Search: Investigators begin a search in an S-pattern from the a border of a crime scene and overlap the S-pattern on return

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Typical types of Crime-Scene Searches

Quadrant or Zone: A small area or room is searched. It's used in homicides, rape, drug and bomb searches. 

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Types of Physical Evidence to Look For:

1. Blood, semen, saliva, sweat 

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2. Hair/Fibers

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3. Documents

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4. Fingerprints

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5. Glass/Paint/Powder Residues

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6. Victim’s clothing

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7. Fingernail Scrapings

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8. Recovered bullets from the body

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Collecting and Packaging Evidence

Physical evidence must be collected and packaged carefully to prevent contamination, breakage, evaporation, and accidental scratching and/or bending.

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Integrity of Evidence

Blood, hairs/fibers, soil and dust should be submitted

intact

and

should not

be removed from garments or surfaces

When these items are found on large objects that cannot be removed easily, evidence can be removed carefully using forceps or swabs

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Integrity of Evidence

Each different item or similar items collected at different locations

must be

placed in separate containers

Prevents damage

Prevents cross-contamination of specimens

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Packaging Evidence

Use forceps for picking up small items

Use unbreakable plastic bottles with pressure lids for hair, glass, fibers, and other small trace evidence

Manila envelopes and screw-cap glass containers may also be used for trace evidence

“Druggist-fold” Envelopes may also be used

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Packaging Evidence

Use wrapping paper, manila envelopes, paper bags are used for blood stained materialAirtight containers are never used because they can readily grow molds and destroy evidenceAirdry wet/bloody clothing and place in paper bags

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Packaging Evidence

Use airtight containers for charred evidence from fires

Prevents evaporation of accelerant

Common packaging:

Empty, unused paint cans

Tightly sealed jars

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Chain of Custody

A list of

all

persons who came into possession of an item of evidence

May include: collector, carrier, lab tech, evidence storage officer, investigator, medical examiner, etc

Unnecessary personnel should not handle evidence without justification

 prevents contamination

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This is an example of a chain of custody tag that should be attached to each piece of evidence to show who all has had possession of the evidence.

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Crime Scene Safety

Increased risk of AIDS and Hepatitis B infection to responding officers at a crime scene

Precautions must be taken for officers to protect themselves from all types of hazards

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Standard/Reference Samples

Physical evidence whose origin is known, such as blood or hair from a suspect, that can be compared with crime scene evidence

Used as a comparison method to incriminate or exonerate a suspect or to identify a victim

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Submitting Evidence to a Lab

May be completed by delivery or by mail

Should be done by someone familiar with the case

Includes an “Evidence Submission Form” stating the case history and type of exam requested

Must maintain Chain of Custody in

all cases

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Evidence Submission Form

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Crime Scene Safety

Increased risk of AIDS and Hepatitis B infection to responding officers at a crime scene

Precautions must be taken for officers to protect themselves from all types of hazards

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Crime Scene Safety: Ways to Reduce Risks

Wear double gloves, protective footwear and clothing

Use masks/respirators, goggles or face shields

Be alert to sharp objects such as knives, needles, razor blades, etc.

Dispose of contaminated objects such as soiled gloves and clothing items that were worn by personnel

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Crime Scene Safety: Ways to Reduce Risks

Complete notetaking with uncontaminated gloves to prevent contamination of pens and notebooks

Remove torn or contaminated material and discard immediately

No eating, drinking or smoking at the scene

All nondisposable linens or clothing should be labeled and laundered properly

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Legal Considerations at the Crime Scene

All removal of evidence from a person or from the scene must conform to the Fourth Amendment:

The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no warrants shall issue, but upon probable cause, supported by oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.

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Warrantless Searches

Existence of emergency situations

Prevent the immediate loss or destruction of evidence

Search of a person or property following a lawful arrest

Search by consent

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Mincey v. Arizona

After a homicide, police searched a scene for four days. Evidence collected was found to be inadmissible in court because the court did not feel that evidence would have been lost or destroyed in the time needed to obtain a legal search warrant.

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Michigan v. Tyler

Fire destroyed a building and evidence was collected the first day at the scene. After the initial entry, later entries into the building produced evidence. All evidence from later entries to the property were deemed inadmissible in court.