Crime Scene Investigations Final

Six basic crime scene activities

1. Recognize the scene

2. Secure the scene

3. Preserve the scene

4. Document the scene

5. Search the scene

6. Collect and pack

Objective of a first responder

1. Ensure safety of victims, office, and bystanders

2. Provider medical assistance if needed

3. Detain Suspects and witnesses

4. Protect and secure the crime scene

5. Prevent contamination or destruction

6. Initiate preliminary documentation

Crime Scene Processing Methodology

1. Preparation

2. Scene Security

3. Initial survey

4. Documentation

5. Systematic search

6. Evidence collection and packaging

7. Final survey

8. Release of the scene

Surface Types for Fingerprint Processing

Non-porous: glass, mental, plastic (powders, cyanoacrylate)

Semi-porous: glossy, cardboard

Porous: paper, fabric, untreated wood (chemical methods like ninhydrin)

Crime Scene Diagrams

Purpose: Show spatial relationships between evidence and the scene.

Must include:

• Title, data, time, location

• Legend/key

• Scale or notation “not to scale”

• Measurements

• Compass (north arrow)

• Evidence labels

• Case number and investigator name

Unpredictable Events at a Crime Scene

• Weather changes (rain, wind, heat)

• Fire, explosion, structural collapse

• Crowd interference

• Animal or insects

• Emergency medical intervention

Conditions and Characteristics of a crime scene

• Size and location

• Indoor vs. outdoor

• Transient (temporary) vs. stable

• Primary vs. secondary scenes

• Lighting, weather, and accessibility

Crime Scene Search

Definition: A systematic examination to location physical evidence.

Methods:

• Line/strip

• Grid

• Spiral

• Zone/quadrant

• Wheel/ray

• Goal: Find, document, and preserve all relevant evidence.

Crime Scene Reconstruction

Definition: Recreating the sequence of events before, during, and after the crime.

Involves:

• Physical evidence

• Bloodstain pattern analysis

• Wound analysis

• Firearm and trajectory analysis

• Witness statements

Mitochondrial DNA vs. Nuclear DNA

Nuclear DNA Mitochondrial DNA

From both parents From mother only

Found in nucleus Found in mitochondria

Highly individual Less discriminating

Common in blood, saliva Useful in hair shafts, bones

Crime Scene Documentation Tasks

• Notes (written observations)

• Photography

• Sketches/diagrams

• Video

Problems with Crime Scene Photography

• Poor lighting

• Incorrect angles

• Missing scale

• Motion blur

• Over- or under-exposure

• Failure to photograph evidence in situation

Avenue of approach considerations

• Avoid disturbing evidence

• Use established path if possible

• Document your entry and exit

• Consider contamination risks

• Follow least intrusive

Final Report Must include

• Case information

• Scene description

• Evidence collected

• Method used

• Observation and findings

• Chain of custody

• Conclusion (facts only, no opinions)

Basics of evidence packaging

• Packaging each item separately

• Use appropriate container (paper vs. plastic)

• Seal and label properly

• Maintain chain of custody

• Prevention cross-contamination

Impression Evidence

Evidence created by contact with a surface, including:

• Footwear impressions

• Tire tracks

• Tool marks

• Bite marks

Buried Remains Investigation Tasks

• Establish a grid

• Use controlled evacuation

• Screen soil

• Document stratigraphy

• Photograph and remains

• Preserve contextual evidence

Documentation a body at a death scene

• Photograph body before movement

• Document position and condition

• Note livor, rigor, and algor mortis

• Record wounds, clothing, and surroundings

• Sketch body location

Livor, Algor, and Rigor Mortis

• Livor mortis: pooling of blood after death

• Algor mortis: body cooling after death

• Rigor mortis: stiffening of muscles after death

Fire Origin and Cause

Origin: where the fire started

Cause: why the fire started (accidental, natural, incendiary)

Problems with Fire Scene Documentation

• Structural instability

• Water damage

• Soot obscuring evidence

• Scene alteration during suppression

• Delayed access

Fire Patterns

• V-patterns

• Burn depth

• Alligatoring

• Spalling

• Smoke and heat movement patterns

Ballistic Evidence Significance

• Cartridge cases: firing pin marks, extractor marks

• Projectiles (bullets): rifling and striations

• Firearms: caliber, class characteristics, function

Striations and Rifling

Rifling: spiral grooves inside a firearms barrel

Striations: microscopic scratches on bullets linking them to a specific firearm

Impact Angle Equation

Impact Angle=arcsin (width/length)

Forensic Linkage Triangle

• Victim

• Suspect Crime Scene

• Suspect

Crime Scene Integrity Issues

• Contamination

• Evidence loss

• Unauthorized access

• Poor documentation

• Improper handling or storage

Scientific Method

1. Observation

2. Question

3. Hypothesis

4. Testing/experimentation

5. Analysis

6. Conclusion

7. Peer review