Grinko.Chapter 9 & 10 Trace Evidence

Trace Evidence

physical evidence found in small amounts

why is trace evidence hard to find?

because they are so small like microscopic amounts to even make a physical match

value of trace evidence

• can corroborate other evidence

• provides links connecting objects, indviduals, and location

what happens if we have a lot of trace evidence?

• the stronger the case

what does trace evidence always require?

comparison of questioned vs. known samples

where is metal usually found or where should investigators look?

soil, metal, floor mats, and contaminating a consumer product

what are the physical properties?

• odor

• color

• density

• boiling point

• solubility

• refractive index

chemical properties meaning?

characteristics that determine how substances change like reactions, acids, and bases

list all chemical properties

• toxicity

• oxidation states

• heat of combustion

• chemical stability

• flammability

• coordination number

• reactivity

• possible chemical bonds

• enthalpy of formation

how do chemists identify substances?

• they use substances, labs

• uses physical and chemical properties

how does identifying a substance help?

• it helps w eliminating a source of link

• provides a relationship

• provides a conection

flame test

• Can be used

  to detect the

  presence of

  metals, salts,

  or chemicals

what flame colors do the following show:

• arsenic

• barium

• calcium

• copper

• lead

• potassium

• sodium

• blue

• light green

• brick red

• blue/green

• blue/white

• lilac

• bright orange

cheiloscopy

study of lip prints

is cheliscopy largely accepted as evidence?

• it’s limited bc of acceptance and credibility

what can cheiloscopy be used for?

identification/association

where can paint be used for?

• vehicular hit & run

  • paint chips left at the crime scene can match w the vehicle

• traces of house paint (forced entry)

  • can compare properties of disturbed paint at crime scenes with suspect’s tools

• art forgery

  • can analyze use of paint and see if they’re real or not authenticity

list 4 coats of paint that new paint has

1. electrocoat primer

2. light/ dark primer

3. base coat

4. clear coat

how much should people zoom when examining cross-section patin

10-40x

if the car is repainted what does it add to?

probative value

what does older paint contain?

lead

why is soil trace evidence?

it can be everywhere and transferred easily

what does comparative analysis look at?

• composition

• density

• magnetism

• ph

• particle size

what’s one of the most comon materials in the world?

• soil

what’s soil?

Complex mixture of different

particles from weathering of rock

and organic material from decay of

vegetation & animals

what’s 4 things that determine the composition of soil?

• climate

• living organisms topography

• parent material

• time

what proportions determine soil’s properties

silt, sand, clay, and organic matter

size of their molecules

sand- long

silt- medium

clay- small

how unique is soil?

• so unique that it would be really diff from the soil a few meters away

why do we use soil?

to compare and find origin of stuff

what’s the locard principle?

soil is everywhere and leaves trace everywhere

why do ppl use glass as trace?

to place suspect at scene

where are glss gragments found in?

in clothes, shoes, in the victim

is glass class or individual?

it’s class but it can be indvidual when it’s pieced together

when’s glass class?

when it’s physical properties make use

nature of glass

• brittle

• hard

• refractive index

• transparent

• amporphous

• composed of silica

t or f all glass fragments can be measured?

false; some are way too small that they don’t fit

what’s the simplest method for measuring the density of glass?

water displacement or floation method

what’s refractive index?

hen light strikes a transparent material, there is a change in its direction

how can glass fragments be matched up?

• by matching refractive indicies

concentric vs. radial

radial is forst, and concentric is second, radial is like rays while concentric is more circular