Lesson 2 Fingerprint Pre-Lesson Reading 1. Fingerprint Principles: According to criminal investigators, the use of fingerprint follows 3 fundamental principles: a. A fingerprint is an individual characteristics because no two fingers have yet been found to possess identical ridge characteristics. b. A fingerprint remains unchanged during an individual’s lifetime. c. Fingerprints have general ridge patterns that permit them to be systematically classified. 2. Origin of fingerprint: a. Take a look at your fingertip. You’ll see small ridges made of skin. The ridges have a purpose. They help you get a better grip on stuff you pick up. b. The ridges develop in the womb and remain the same throughout life, barring some sort of scarring or trauma to the deep skin layer. Although people grow and increase in size, the ridges became permanent and fixed in their patterns from about 17 weeks of embryonic development, ridge patterns do not change like other parts of our bodies. c. When the finger touches a surface, perspiration and oils are transferred onto that surface, leaving a pattern called fingerprints. 3. All fingerprints are classified into three categories on the basis of their general patterns : a. Arches Ridges enter on one side and exit on the other side. Approximately 6% of people exhibit this pattern 1
Transcript
Lesson 2 Fingerprint
Pre-Lesson Reading
1. Fingerprint Principles:
According to criminal investigators, the use of fingerprint follows 3 fundamental
principles:
a. A fingerprint is an individual characteristics because no two fingers have
yet been found to possess identical ridge characteristics.
b. A fingerprint remains unchanged during an individual’s lifetime.
c. Fingerprints have general ridge patterns that permit them to be
systematically classified.
2. Origin of fingerprint:
a. Take a look at your fingertip. You’ll see small ridges made of skin. The
ridges have a purpose. They help you get a better grip on stuff you pick
up.
b. The ridges develop in the womb and remain the same throughout life,
barring some sort of scarring or trauma to the deep skin layer. Although
people grow and increase in size, the ridges became permanent and fixed
in their patterns from about 17 weeks of embryonic development, ridge
patterns do not change like other parts of our bodies.
c. When the finger touches a surface, perspiration and oils are transferred
onto that surface, leaving a pattern called fingerprints.
3. All fingerprints are classified into three categories on the basis of their general
patterns:
a. Arches
Ridges enter on one side and exit on the other side.
Approximately 6% of people exhibit this pattern
b. Loops
Ridges enter on one side and exit on the SAME side.
Approximately 60% of people exhibit this pattern1
c. Whorls
Consists of circles, spirals.
Approximately 34% of people exhibit this pattern
4. Types of fingerprint evidence:
a. Patent prints
These are clearly visible. They’re made when you touch something like
paint or blood and then touch other surfaces.
b. Latent prints
They’re formed when you touch something and the oil and sweat on your
hand leaves a print. Latent prints are mostly invisible to the naked eye.
Fingerprinting dust makes them visible.
c. Physical prints
These are made when you touch something like gum that leaves a clear
impression of your prints.
5. Three common methods of latent print enhancement :
a. Lifting powder Application
Work bests upon smooth solid surface, e.g. walls, glass, knife.
Fingerprint powders are colored, fluorescent, or magnetic materials
that are very finely ground and are brushed lightly over a suspected
print to produce contrast to the background. These powders typically
are available in black, white and other colors, including metallic.
Once the lifting powder has been successfully applied a fingerprint is
then “lifted” using a wide piece of clear smooth tape.
b. Iodine Fumigation2
Work bests upon light-colored light weight/low density objects, e.g.
paper, fabrics
A small amount of iodine is placed at the bottom of a glass chamber.
The object bearing the suspected latent prints is then suspended from
the top of the chamber. The chamber is then sealed and chemical
reaction occurs. The latent fingerprints become dark brown in colour
and photograph of the fingerprint will be taken.
WARNING: Iodine is irritating to skin and eyes. Do not breathe in iodine
vapours.
c. Cryanoacrylate Fumigation
Cryanoacrylate is a very strong glue. It has tendency to stick to the
body oil residue found in fingerprints.
Work bests upon dark-colored dense objects, e.g. guns, knife handles.
When Cryanoacrylate begins to react with the body oil residue in a
fingerprint, it leaves behind a whitish-grey film which is visible to the
human eye. Photograph of the fingerprint will be taken.
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Lesson 2 Fingerprints
Worksheet 2.1 Fingerprint Basics
1. Classify each of the following prints as loop, whorl or arch.
a. b. c.
2. While searching a murder scene, you believe the following items may contain
latent fingerprints. Indicate whether prints on each item should be developed
using fingerprint powder or chemicals.
a. A leather sofa
b. A mirror
c. A painted wooden knife handle
d. Blood-soaked newspapers
3. Fingerprints that deposited on a surface when oils and sweat are excreted from
pores on the friction ridges are called ________________ fingerprints.
4. The most common fingerprint pattern is the _________________ .
5. True or False
a. The individuality of a fingerprint is determined by its pattern.
b. Fingerprints cannot be changed during a person’s lifetime.
c. Arches have type lines, deltas and cores.
d. Identical twins have the same fingerprints.
e. Computerised fingerprint search systems match prints by
comparing the positions of bifurcations (分岔) and ridge
endings.
f. A fingerprint left by a person with soiled or stained fingertips is
called a latent print.
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Lesson 2 Fingerprints
Worksheet 2.2 Practice the identification skills
Figure 1 ______________________________
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e.g. fork
Instruction:
1. Examine the fingerprint (Figure 1) with a magnifying glass if necessary.
2. To which class does the fingerprint pattern belong? Write down your answer.
3. Use Table 1 to help identify fingerprint ridgeline details. Locate and label at
least 8 positions of ridgeline details in Figure 1.
Table 1 Fingerprint ridge details
Fork
Double Fork
Triple Fork
Delta
Dot
Bridge
Hook
Eye
Short Ridge
Ending Ridge
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Lesson 2 Fingerprints
Worksheet 2.3 Mak e a fingerprint
Apparatus and Materials:
(per group)
2 2B pencils
2 pieces of white paper
1 bottle of fine iron powder
1 adhesive tape
1 handkerchief
4 microscope slides
1 magnifying glass
Procedures:
Part 1 Patent fingerprinting
1. Rub a 2B pencil over a piece of white paper until it is covered with graphite.
2. Rub your index finger against your nose or forehead and place the finger at the
center of the microscope slide.
3. Press and roll your index finger firmly on the graphite pad and then press the
finger on the tape thoroughly.
4. Place the fingerprint on the worksheet.
5. Repeat step 2 to 4 for another index finger.
Part 2 Latent Fingerprinting
6. Use a handkerchief to wipe a microscope slide free of any stray fingerprints.
Handle the slide only by the edges.
7. Rub your index finger against your nose or forehead and place the finger at the
center of the microscope slide.
8. Sprinkle the iron powder onto the edge of the print.
9. Lightly shake the slide to apply a thin coating of iron powder onto the latent
print.
10. As the print becomes visible, you should shake the slide lightly until there is no
excess iron powder on the slide.
11. To lift the fingerprint from the slide, you should position the untouched portion
of the tape above the imaged fingerprint and smooth the tape over the developed
print.
12. Place the fingerprint on the worksheet.7
13. Repeat step 7 to 13 for the rest of your fingers.
Part 3 Statistics
14. Identify the pattern of each your fingerprint.
15. Write down the name of pattern under each fingerprint.
16. Count the numbers of each pattern.
Part 4 I dentif y the ridgeline details
17. Choose the fingerprint with best resolution among all your fingerprints.
18. Examine the fingerprint with a magnifying glass.
19. Use Table 1 of Worksheet 2.2 to help identify different fingerprint ridgeline
details.
Results:
1. Direct prints of your fingers
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2. Latent prints of your thumb and index finger
3. Among all your fingerprints, the numbers of each pattern are as follows:
No. of Arches： __________
No. of Loops： __________
No. of Whorls： __________
Do all your fingerprints have the same pattern? ________________
4. List out the names of ridgeline details you can identify. Count the frequency of
each ridgeline detail.
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Group discussions
1. Count the number of patterns of all fingerprints among your group. What is the
population percentage of each pattern? Show your calculations.
2. Which pattern is most common among your group members?
3. Which colour is the most popular color for fingerprint powder? Why?
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Lesson 2 Fingerprints
Worksheet 2.4 Try out the steps in analy s ing and comparing fingerprints
Case Profile
A suspect was arrested in a burglary case. When the suspect was
fingerprinted, the desk sergeant noticed something very unusual – his
fingerprints somehow had been altered. The suspect admitted that he had
peeled off the skin from one of his thumbs and transplanted it onto another
thumb. The suspect even claimed that “I have new thumbprints. I am a clean
person.”
Furthermore, the police have recovered an excellent latent thumbprint from an
unsolved burglary case 3 years ago. There are some indications that these 2
cases may be related.
The recovered print and the suspect’s new thumbprints are provided for your analysis.
Can a match be made between the direct thumbprints from the suspect and the latent
thumbprint found at the crime scene? Imagine you are fingerprint examiner and you
need to evaluate the presented evidence, reach conclusions and provide findings in a
report to the law enforcement authorities and the court.
Known left
thumbprint from suspect Known right thumbprint from suspect
Recovered print from burglary
scene
The five steps in analy s ing and comparing
fingerprints :
Step 1: Identify the general type of the central
area of the fingerprint.
Step 2: Match fingerprint ridgeline details.
Step 3: Compare the unknown print and the
known print, point by point, feature by
feature, to see if they match.
Step 4: Evaluate whether the unknown print
matches the known print or not.
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Step 5: A second examiner verifies the results.
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Report
Known left thumbprint from suspect
Known right thumbprint
from suspect
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Recovered print from
burglary scene
Can the suspect be identified? Summarise your findings and report conclusions to law
enforcement authorities and the court.
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Lesson 2 Fingerprints
Follow-up Activities
1. Case study: Fingerprints on 2004 Madrid train bomb bag traced to Algerian
“Fingerprints found in a plastic bag containing detonators of the kind used in
the March 11 Madrid train bombings were identified as belonging to an
Algerian national, police said Thursday evening..”.
Read the following or related articles and discuss what’s wrong with FBI.
