forensic test 1

tool marks

Leaves indentations, scratches, or cut marks

Leaves distinctive marks when forced against another surface

Can link a suspect to a crime scene

basic premise of tool mark identification

All objects are unique and can be differentiated from one another.

Harder objects impart features on softer objects

irregularities make each tool unique

Produced during manufacture

Can be made by wear from use

Can distinguish one tool from another

markings

Nicks, Ridge marks, Blemishes, Foreign material, Rust

indentation mark

when pressed against a softer surface, A negative impression of the tool, made by prying open an item (cash register, box, window, door), Size and shape of the tool may be determined by measuring the impression

abrasion mark

harder surface sliding along softer surface

cutting mark

Left on edge of a surface as it is cut

photographing tool marks

oblique lighting (casts shadows and highlights details)

preserving tool mark evidence

Photograph impression

Photograph and remove trace evidence

Make a cast of the impression

analyzing tool mark evidence

The goal of tool mark analysis is to identify the major unique characteristics; should never be fitted togther!

serial numbers

May be stamped or printed on tools

Used to trace a tool to the manufacturer

May be traced to the store where purchased

Recovering partially removed serial numbers has become an important forensic technique

tool mark evidence in court

Tool itself or actual tool mark can be presented in court

Casts and magnified images of toolmark comparisons can also be presented at trial

In response to a 2000 Florida court case that established tool mark evidence being inconclusive

Ames Lab 3d characterization

No contact with the tool

Magnifies, scans, and measures surface contour map of the marks

impression evidence

considered to be class evidence unless there are unique and distinguishing characteristics that make it individual.

what type of evidence is dental work

individual evidence

dental impressions

only circumstantial evidence

patent impressions

Visible (object picks up soil, dist, paint, blood, or other material and transfers it)

plastic impressions

left in soft materials (snow, mud, soil, or blood)

latent impressions

Hidden from the unaided eye; Made visible through dusting, electrostatic techniques or with chemicals

shoe and foot impressions answer questions

What were the entrance and exit routes?

How many people were at the crime scene?

Were the people moving? If so, what direction?

tread pattern

Shoe size, type of shoe

wear patterns

factors that personalize footwear, shape of foot, body weight, pressure on outside of heel rather than inside, unique holes, cuts and debris

gait

a pattern of moving

stride

the length of one step

photographing

Take photos in situ (as it appears)

Lens perpendicular to the impression to reduce distortion

Indirect/oblique

lifting impressions

luminol or blue star, powders

casting

dental stone, plaster of paris

two dimensional prints

Dirt or other material picked up by the shoe and deposited onto a flat, hard surface, impressions left behind in dust, wax, polish

three dimensional prints

made in soft materials like dirt or snow

ribs

ridges running around the circumference of the tire

grooves

indentations

track width

measured from the center of the tread of a tire to the center of the tread on the opposite tire

wheelbase

distance between the center of the front wheel and the center of the rear wheel

how long should tire impression collections be

at least 3 meters long to ensure the tires make a complete rotation

skid marks

accelerating or decelerating quickly, Dark to light or light to dark, Leaves straight tire marks

yaw marks

tire rolls but simultaneously; always curved, stripes form on pavement as tire is dragged laterally

tire scrubs

used to determine area of impact

When bite marks are found on the skin (which is somewhat elastic) or stretchable clothing

the accuracy of measurements is always in question

for dental evidence to be admissible in court

at least two forensic dental experts must agree on the identification

natural fibers

plants, animals, minerals

animal fibers

hair, fur, silk. all made of proteins such as keratin

plant fibers

seeds, fruits, stems, leaves. all contain cellulose

mineral fibers

neither proteins nor cellulose; crystalline materials; fiberglass or asbestos

synthetic fibers

originate from petroleum products; nylon, polyester

fiber

the smallest unit of a textile material that has a length of at least 100 times greater than its diameter

yarn

short fibers that are spun together. A very thin yarn is called a thread

rope

very thick yarn

what do forensic scientists look at in fiber

twist direction

warp

the arrangement of threads lengthwise side by side and close together

weft

crosswise threads that are pushed back and forth

weave pattern

the pattern in which the weft passes over and under the warp; plain, twin, satin

thread count

number of horizontal weft and and vertical warp threads in a square inch of fabric

type of evidence fibers are

class evidence

direct transfer

when fibers are transferred from one person or object to another person or object

secondary transfer

when a fiber is transferred from an object or person who then transfers it to a second person

collecting fiber

Collection in the field and in the lab using tape, forceps, and sticky lint roller

Forensic scientist considerations

type and color; number and where they were found; textile; time between crime and discovery of fiber

fiber evidence

With only one fiber as evidence, it cannot be damaged or altered through testing.

sir francis galton

found fingerprints were unique and dont change with age

ivan vucetich

first practical use by law enforcement

sir edmund henry

developed own classification system based on pattern types

AFIS

automatic fingerprint identification system; ability to store millions of fingerprints and search for them in minutes

biology of fingerprints

Volar pads (swelling of underlying tissue on hands and feet) begins about the 6th week)

Friction ridges begin to form about 10th week of gestation

3 layers of skin

Epidermis (Outermost protective layer)

Dermis (Middle layer, Provides elasticity)

Hypodermis (Innermost layer)

Basal layer of epidermis

single layer of cells

alive and reproducing

cells migrate to the surface (30 days)

Top layer contains 25-30 layers of dead, flattened skin cells that continually slough off

changing fingerprints

injuries to skin wont change fingerprints; if basal layer is damaged then there is new ridges developing

fingerprint residue

natural secretions, environment, eccrine glands, sebaceous glands

patent fingerprint

visible prints

plastic fingerprint

actual indentations left in soft material like clay

latent fingerprint

most common; hidden prints can be made visible by use of powder or chemicals

ACE-V

Analysis

Comparison

Evaluation

Verification

The examination method used in forensic identification

core

center most print

delta

triangular area where ridges extend in 3 directions

ridge count

number of ridges between the core and the delta; dont count core or delta

loop pattern type

65% of population. exit on the same side entered

whorl

30% of population has whorls; series of concentric circles

arch

5% of the population; ridges enter on one side of the print, exit on the other

minutiae

unique small details

bifurcation

The point where one ridge divides, or forks, and splits into two ridges (like letter Y)

dot

a ridge that is a big as it is wide

ending ridge

a ridge that stops within the ridge structure

enclosure (island)

the point where one ridge splits, becomes two for a short time, then comes back together

pores

Can vary in size and shape (round, oval, square) or resemble a notch on the edge

edges

Can be affected by various factors (pressure, dev. agents, foreign material) so it's difficult to make matches

photography for collecting prints

Photographed in situ (in its original place and state)

fingerprint powder

Fingerprint powders are fine powders used in dusting for prints by CSI’s.

magnetic powder

the powder is attracted by the magnet in the head of the magnetic brush, causing the iron particles to form a kind of brush.

superglue

Produces a visible, sticky white material that forms along the ridges of the fingerprint

alternative light source

Use to enhance the appearance of a fingerprint

ninhydrin

Typically used with paper and other porous surfaces

Reacts with latent print residue like amino acids

Produces a purple color

why no prints?

Surface (porous vs non porous)

Barriers

Temperature (heat and cold) and humidity

Light and water

forensic

from latin word forensics, which means of the forum

forensic science

using science to help resolve legal matters

qualitative data

subjective, uses our senses

quantitative data

objective, data than can be measured

forensic investigator must convince a jury that evidence is

scientific, reliable, valid

forensic investigator

collects physical evidence, reports to law enforcement, possibly testify

observation

gathering information through senses; done largely without thinking

perception

interpreting sensory observations

factors that affect eyewitness accuracy

Fatigue and stress

Distractions (cell phone, etc)

Emotional state (anxiety, fear); Uninvolved bystanders may be more accurate

Time

Individual perceptions