crime scene investigation

what constitutes a crime scene?

Any area where illegal activity has occurred and where physical evidence can be found.

once recognized as a crime scene there is a sequence

1. securing the crime scene

2. recording the crime scene

3. searching for evidence

4. recording, preserving, and storing the evidence

Securing the scene

First person at the scene is the responder, who must ensure safety and preserve the area from contamination or disturbance.

Who are typically the first responders?

police officers, emergency medical personnel, fire department

What happens after health and safety is secure?

The responder secures the crime scene by isolating the scene and controlling movement in and out of the scene, they also document initial observations.

Recording the scene

once the scene is secure the investigators take over and are responsible for recording/documenting the crime scene, identifying evidence, and collecting evidence.

Video recording (typically occurs first)

entrance and exits, wide angle views, orientation of evidence, record victims viewpoint from multiple directions. critical because the scene changes with time.hP

Photography of the scene

mid-range, and close up views of evidence locations and orientation,including overall shots to provide context and relationships between items. Essential for thorough documentation of the crime scene.

sketching the crime scene

captures spatial relationships within the scene.

Other recording techniques involve:

3D scanning as an alternative to sketching, LIDAR which is light detection and ranging.

Searching for evidence

occurs after the recording of the scene, looking for objects that could be involved in the crime or help to solve the crime.

Where can evidence searches occur?

They can occur at the crime scene and back in the lab.

Search patterns include:

• strip or line

• grid

• spiral

• wheel or ray

• quadrant or zone

Why does searching for evidence require training and experience?

Searching for evidence can be considered difficult when it comes to weighing what objects actually matter, knowing how to use the tools, and proper packaging of items.

ALS alternative light source

works by directing light at different wavelengths towards surface, causing certain compounds to “fluoresce”

What can UV light show?

semen, urine, blood, vaginal secretions, hair, other fibers, possible bacterial cells, spores.

What does blue-green light show?

bone fragments, teeth, latent prints w or w/o enhancements, some hair and other fibers, bruises, bite marks.

What can infrared light show?

questioned documents, bite marks, bruises(depth dependent)

Collecting evidence

occurs after searching for evidence and determining what pieces are crucial to the case. Sometimes there is a limit of items allowed to be submitted per case.

Evidence Collection

Evidence has to be handles in a way that prevents any changes from happening between when it is collected and when it arrives at the lab.

Manila envelopes and sealable plastic bags

used for most trace evidence

unbreakable plastic constainers with screw cap lids

good for hairs, fibers, glass, and other small trace evidence

Metal paint cans

debris from a fire to prevent evaporation of volatile chemicals

chain of custody

a log of who has posession of a piece of evidence and when