Module 1 Types of Evidence & Fingerprint Analysis Flashcards
Types of physical evidence
Identified and Individualized
Fingerprints
Hair
Blood
Bullet casings
Paint fragments
Fibers
Individualized physical evidence
Unique can be directly linked to specific person or source Finger prints , DNA , bullet casings, dental impressions
Identified physical evidence
Common source into crossing items having some more properties Clothing, shoe print, blood type Useful in 2 ways When directly supports individualized evidence And/or When presented with additional pieces of identified evidence
Finding an interpreting physical evidence from a crime scene is crucial because it can?
Prove a crime has been committed
Establish identity of the suspect(s)
Exonerate the innocent
Corroborate the victims testimony
Lead to a confession from suspect
More reliable than eyewitness
Expected by Judge/ juries
What are the 3 types of finger prints
Visible
Latent
Physical
What is a Visible Print ?
Easily seen by human eye
May be left on an object at crime scene b/c of Blood Perspiration Dirt/oils on hands
Latent
Hidden or concealed in some way Not visible to naked eye Most are composed of perspiration and/or body oils
Latent fingerprints are those that are not apparent to the eye but can be made sufficiently visible, as by dusting or fuming, for use in identification
Physical
When distinct impression is left upon soft materials such as… Wax Food items Caulking around window/doors
What are the 2 layers of the skin where prints are?
Skin is made up of 2 layers The outer layer EPIDERMIS Inner layer DERMIS Burns or abrasions cuts don’t alter ridge pattern If a cut is deep enuf it can damage the dermis causing a scar
Epidermis
Where fingerprint ridges are found
Dermis
contains sweat glands
3 main types of ridge patterns are?
Arches
Loops
Whorls
Arch sub-classifications
Plain/simple arch Tented arch
Loop sub-classifications
Ulnar loop Radial loop Double/twinned loop
Whorl sub-classifications
Plain whorl
Central pocket whorl
Accidental whorl
what % of the population has each type of print
Arches 6% of people (rarest)
Whorls 34% of people
Loops 60% of people
How is a fingerprint match made ?
print identification isn’t determined solely by its pattern,
but also by careful analysis of points within the pattern called ridge characteristics or minutiae.
average print has more than 100 unique ridge characteristics or minutiae.
Identification of 8-16 ridge characteristics within a print is used to match a print to a suspect.
What is lifting powder \use of this powder
Lifting powders are made of one type of metal, or homogeneous mixtures of metals.
Lifting powder application is useful to enhance fingerprints that have been left upon hard surfaces. They work best upon smooth, solid surfaces
What safety precautions should be used when working with lifting powder?
Inhalation of metal lifting powders can be harmful to the tissue of the lungs;
Protective goggles and mask should be worn.
How are prints lifted when using lifting powder ?
After lifting powder has been applied, a fingerprint is ‘lifted’ using a wide piece of clear smooth tape.
Afterwards, the print is analyzed by forensic experts.
How do Forensic experts choose lifting powders ?
Individual preference
Availability
Cost
What are lifting powders applyed with ?
In the early days of crime scene investigation, lifting powders were gently applied using feathers.
Today, specialized brushes that contain very soft bristles such as bird feathers, squirrel hair, camel hair, or fibreglass are used
Another type of lifting powder brush has a strong magnet at the end to attract the metal-based lifting powder not sticking to the surface as it is applied.
How dose lifting powder work ?
The scientific principle of lifting powders is that the positively-charged metal powder is attracted to the predominately negatively-charged body oil residue in sweat that is found in a fingertip impression. The powder is highly attracted to the oily, negatively-charged fingerprint residue but not to the surrounding surfaces.
What is Iodine Fumigation ?
The related reaction is iodine fumigation enhances fingerprints
that have been left upon light-coloured, light weight, and low density objects such as paper, some types of fabrics such as light-weight cottons and some polyesters.
simple technique, a small amount of iodine is placed in the bottom of a glass chamber
object bearing the suspected latent prints is suspended from the top of the chamber.
chamber is then sealed,
and the above reaction occurs if sodium chloride (sweat) is present.
After a reaction occurs, the prints are then exposed to a fixing solution (a mixture of cyclohexane and dichloromethane) that causes the prints to turn dark-blue.
The prints now become permanent.
If a fixing solution is not applied, the exposed fingerprints begin to degrade after the object has been removed from the glass chamber.
where results are often ready within a few minutes,
Reaction and reasoning behind Iodine Fumigation
sweat contains sodium chloride - NaCl - an ionic compound composed of a single sodium cation (Na+) attracted to a single chloride anion (Cl-). Sodium chloride is a salt - hence the reason sweat tastes salty. Within fingerprint residue, and especially within sweat, many sodium cations occur (Na+).
All negatively-charged anions are highly attracted to positively-charged cations. Iodine in its pure state is a non-metal solid that produces negatively-charged anions (I-). So when iodine is exposed to the sodium chloride in sweat, a single replacement reaction occurs in which the iodine displaces the chloride ions and attaches to the sodium ions to produce sodium iodide (NaI).
Cyanoacrylate Fumigation
Cyanoacrylate(main component of a strong glue) enhances latent fingerprints
when Cyanoacrylate reacts with the body oil residue in a fingerprint, it produces a visible whitish-grey film that is especially noticeable on dark-coloured objects.
prints that have been left upon solid objects that are smooth surface or slightly textured surface such as metals ,knife ,handles, guns, bullet cartridges, pop cans) hard plastics such as credit cards, knife handles, guns)
visible prints from cyanoacrylate fumigation can take from one to 24 hours or more.
After a reaction does occur, the object is removed and is analyzed and/or photographed. An advantage to prints enhanced by cyanoacrylate is that they do not degrade. They are permanent records.This type of print cannot be lifted, so it must be photographed for analysis.
small amount of cyanoacrylate is placed in the bottom of a closed chamber
.The object bearing the latent prints is suspended in the top of the chamber.
The chamber is then sealed,
and heat and moisture are introduced (For example, a light bulb or warming plate and a cup of water are adequate)
Over time, a reaction occurs causing the cyanoacrylate to change from a liquid to a gas (sublimation). It is attracted to any body oil residue present in the chamber.
Short-term vs. Long-term Latent Fingerprint Samples
Fingerprint impressions can remain in place for a surprisingly long time. Even exposure to the elements such as heat, cold, and moisture very often will not destroy a fingerprint impression. However, a smudged fingerprint impression is typically of little value to forensic experts. Smudging occurs if pressure has been placed upon the fingerprint impression or when the subject’s finger slides across a surfac
Experiment 1 Solutions
Experiment 2 Solutions
What kind of print is this ?
What type of print is this ?
What type of print is this?
What print is this?
What is this print?
