Monday, 12/16Homework Quiz

1. Take out your notes (HW) and keep it at your desk.

2. Take a quarter sheet of scratch paper and put your name and class period on the top.

3. You do not need to copy the questions, your responses do not have to be in

complete sentences.

1. List the three types of fingerprints that are found at crime scenes.

2. What does RUVIS stand for and what is it used for?

3. What are three types of powders used to develop prints?

4. Which type of chemical treatment was developed first?

5. What is the first thing that a criminalist must do after visualizing a print but before any attempts are made to preserve it?

When you are done:Put your quiz in the HW folderKeep your notes at your desk

Methods Of Detecting Fingerprints

Objectives:1. Distinguish visible, plastic, and

latent fingerprints.2. List the techniques for developing

latent fingerprints on porous and nonporous objects.

3. Describe the proper procedures for preserving a developed latent fingerprint.

Distinguish visible, plastic, and latent fingerprints.

O Visible prints: Made when the finger deposits a visible material such as ink, dirt, or blood onto a surface

O Plastic prints: Fingerprints impressed into a soft surface

O Latent (invisible) prints: Caused by the transfer of body perspiration or oils present on finger ridges to the surface of an object

Locating Fingerprints

O The method of visualization is determined by the type of surface being examined:O Hard/nonporous surfaces: Powders and

Super Glue fumingO Soft/porous surfaces: Chemical treatment

O RUVIS (Reflected Ultraviolet Imaging System)O Aims UV light onto a non-absorbent surface

to help locate fingerprintsO Prints are then developed in the

appropriate manner

List the techniques for developing latent fingerprints on porous and non-porous surfaces.

O Powders (grey/black, metallic, fluorescent)

O Chemical methods:O Iodine fumingO NinhydrinO Physical developerO Super Glue fumingO DFO

O Fluorescence

PowdersO Used mostly on dry, nonporous surfacesO Applied with camel’s hair or fiberglass brushO Powders adhere to the perspiration and oil

residues left by the ridgesO Grey/black:

O Most commonO Used on lighter surfaces

O Magnetic:O Less damaging to printO Good for leather and rough plastics

O Fluorescent:O Used in conjunction with UV lightO Prevents prints from being obscured by color of the

surface

Iodine FumingO Oldest of the chemical methodsO Process:

O Iodine crystals and suspect material placed in a cabinet and heatedO Iodine goes directly from solid crystals to a gas

(sublimation) when heatedO Vapors combine w/ the print to make it visibleO It is thought that the iodine combines with fatty

oils or residual water in the fingerprint, but not known for sure

O Prints that are developed using iodine fuming are not permanentO Can be extended by a month to a year with the

application of a 1% solution of starch in water

NinhydrinO Process:

O Sprayed onto porous surfacesO Frequently used on paper

documentsO Purple/blue prints will

appear w/in 1 to 2 hours after application

O Chemical reaction occurs with amino acids in the deposited perspiration

Physical DeveloperO Silver nitrate-based liquidO Used for visualizing latent prints

undetected by previous methodsO Good for porous materials that may have

been wet at one timeO Should be the LAST method used

O Washes away traces of proteins from an object’s surface

O Order of application:

Iodine Ninhydrin Physical developer

Super Glue FumingO Most useful for nonporous surfaces such as

metals and plasticsO Process:

O Super Glue (cyanoacrylate) heated in enclosed chamber with suspect material

O Expose for about 6 hoursO Is developed when the glue adheres to the

print and gives it a white appearanceO Fuming wands are available for more

convenient development on larger surfacesO Has been used to develop prints in small,

enclosed areas such as the inside of a car

Super Glue Fuming

FluorescenceO 1st – Discovered that fingerprints could be

visualized by exposure to laser lightO 2nd – Fingerprints could be treated with

chemicals that would induce fluorescence when exposed to laser lightO Chemicals that could be applied after

development (zinc chloride after ninhydrin, rhodamine G6 after Super Glue fuming)

O 3rd – Lasers were no longer needed to induce fluorescence as it was now chemically induced, and high-intensity or alternate light sources could be used to visualize prints

High-intensity

Alternative light sources

O Quartz halogenO Xenon-arcO Focused using

fiber-optic cablesO Can utilize several

filters giving the flexibility to select different wavelengths of light

O Light-emitting diodes (LEDs)

O More portable

Additional Processing Information

O Chemical agents do not interfere with DNA tests

O Ideally, all processing and development of prints should be done in the laboratory and NOT at the crime scene

Preservation of Developed Prints

O Once developed, fingerprints must be preserved

O Before preservation fingerprints must be photographed FIRST!O Close-up of fingerprintO Expanded shot for overall location of the

fingerprintO 2 possible procedures:

O Small objects:O Preserve object w/ print in its entiretyO Cover print w/ cellophane

O Large objects:O If developed w/ powder, lift print w/ adhesive

Digital Imagining For Enhancement

O Photographs are turned into digital filesO The larger the # of pixels, the more

closely the file will resemble the real-world image

O Allows for the removal of background color interference

O More reliable hits in AFISO Easy creation of fingerprint comparison

charts

Digital Imagining For Enhancement