forensics impression evidence

patent impression

• 2D

• an impression visible to the unaided eye

latent impression

•2D

•an impression requiring special treatment (chemicals) to be visible to the unaided eye

plastic impression

•3D

•an impression in soft materials such as soil, snow, or congealing blood, and mud

What questions can shoe, and foot impressions answer to provide clues about the crime scene?

1. how many people were at the crime scene?

2. were people moving?

3. what direction were they moving in?

4. what entrance and exit routes?

5. is there evidence of anyone sustaining injuries at the crime scene?

what information about an individual can be revealed from impressions?

•shoe size

•height of person

•weight

•gait

What info does the databases contain and what can they tell investigators?

• contains names of specific manufacturers and tread pattern used to identify different types of shoes

• crime scene investigators can search to find: manufacturer and company that produced the sole and bought sole for shoe

what factors can help personalize shoe wear patterns?

• shape of foot

• body weight

• activity types

• what surface they walk

• if toes point out/in

• pressure outside/inside heel

• holes, cuts, debris on shoe

What is the difference between gait and tracks?

gait: a persons pattern of moving

track: if persons running, walking, injured, older/disabled: movement of feet going toward direction

step 1: photographing

1. take photograph with and without ruler

2. fill cameras viewfinder with impression

3. take photograph with lens perpendicular to print/evidence

step 2: lifting latent

several different methods used

1. luminol (blood)

2. dusting (make visible footprint/print)

3. electrostatic lifting and gel lifting

step 3: casting plastic

• if impression in sand or soil, plaster of paris impression is made

• if impression in snow, casting material is called dental stone

What is the difference between luminol, dusting, and electrostatic/ gel-lifting?

• luminol: chemical spray, apply on surface uses uv light

• dusting: powder use to reveal impressions

• electrostatic: uses charge to hold dust particles of latent print in place

• gel: gel sandwiched between paper/plastic cover sheet

What 2 characteristics do forensic scientists examine tire tread and impressions for?

tread pattern

wear characteristics

(track width wheel base)

What situations cause the following type of tire impressions?

PATENT

• after vehicle has driven through a fluid like oil, tar, or blood after abruptly accelerating or stopping

What situations cause the following type of tire impressions?

LATENT

• on asphalt or concrete roads by manufacturers oils used to keep tires soft and pliable

What situations cause the following type of tire impressions?

PLASTIC

• off-road surfaces, mud, grass, sand, and snow

The anatomy of a tire is made up of ribs and grooves. What is the difference between ribs and grooves? What is the purpose of ribs and grooves on a tire?

ribs: ridges running around circumference of tire

grooves: indentations

purpose: to channel water away and provide traction as surface makes contact with road/ground

Refer to Figure 16-10 and label the following parts of a tire tread:

Refer to Figure 16-11 in your textbook Label the diagram below:

What are 5 ways to forensically establish car movements?

Skid marks

Yaw marks

Tire scrubs

Indentation Marks

Abrasion Marks

Cutting Marks