Document-Examination. Forensic science ppt

Forensic - Questioned Document Examination

1. Forensic Science

2. 4
th
Amendment
The right of the people to be secure in their
persons, houses, papers, and effects, against
unreasonable searches and seizures, shall not be
violated, and no Warrants shall issue, but upon
probable cause, supported by Oath or
affirmation, and particularly describing the place
to be searched, and the persons or things to be
seized.

3. The Document Examiner
Usually asked to determine if a document is
‘authentic’
Questioned Document – any handwritten or
typewritten document whose source or
authenticity is in doubt
Takes years of training and experience to
become good at comparing characteristics
The uniqueness of handwriting can be considered
individualized evidence

4. Comparing Handwriting –
General Style
First learning to write involves copying a style
from a teacher
Page 556 Figure 16-1
At this early stage handwriting of different
students is very similar
As a person grows up they start personalizing
their handwriting styles without even thinking
about it

5. Comparing Handwriting -
Variations
Variations expected in:
Angularity, slope, speed, pressure, letter and word
spacings, relative dimensions of letters, connections,
pen movement and writing skill
Also differences in WHERE someone writes on the paper
(how close to the margins, how far above the line, etc)
Each type of variation may not be unique to a person,
but the combinations of variations is
How many “matches” between evidence and a
reference sample it takes to make a definite
authentication depends on the scientist

6. Challenges to Comparing
Handwriting
The biggest challenge is when not enough reference
or “known” samples are received for comparison.
Another frequent problem is when questioned
documents only contain a few words or those words
are carefully written to have fewer of the writer’s
individual characteristics
Frequently done with threatening letters, etc
When there is enough writing for comparison, the
attempt to hide individualizing characteristics may
fail
Page 557 Figure 16-2

7. Collecting Writing Samples
Writing samples (exemplars):
 Should contain as many as the same words as possible
Should be written on the same type of paper with the
same utensil
There should be enough exemplars to show the
natural variations in the writer’s style.
P 559 Figure 16-3
The exemplars should have been written around the
same time as the evidence
Ex: can’t compare writing from when a suspect was 12
to when he was 20

8. Getting an Accurate Exemplar
The writer should sit comfortably at a desk or
table and not be distracted.
The writer should NOT be shown the questioned
document.
The writer should be given a pen and paper
similar to those used for the questioned document.
The exemplar should contain the same words or
letter combinations as the questioned document.
Should be written at least 3 times.
Make writer write other things along with a
signature. (like a check)

9. Comparing Typescript
Documents
The examiner may have to identify what brand
of printer or fax, etc was used to produce a
document
If test samples need to be printed, usually
around 10 are printed to show the machine’s
characteristics

10. Comparing Photocopied
Documents
Comparisons usually involve looking at defect
marks made by debris on the glass surface, inner
cover or mechanical portions of a copier

11. Comparing Faxed Documents
Most important to study and compare the header
(Transmitting Terminal Identifier)
P 562 Figure 16-4
Can be faked, but microscopic examination
usually reveals the falsity
Can use the header to determine the machine’s
model

12. Comparing Computer Printed
Documents
When there is a suspect machine, comparisons of
markings can help determine the origin of a
questioned document
When there is not a suspect machine, work can
be done to identify the printer model used:
Examine the toner with a microscope
Find the chemical compounds within a toner
Find the type of paper used
The method used to apply the toner to the paper
EX: ink-jet, thermal transfer, laser printers, etc

13. Comparing Typewritten
Documents
Finding the make and model of typewriter used:
Compare to databases of what typeface is used, what
style of letters, etc
Finding out if a suspect machine produced specific
evidence:
Does the normal wear and damage to the machine
match? Ex: are the letters misaligned identically
Full word-for-word examples can be compared to see
if the defects match (p 563 Figure 16-5)
The ribbon can be studied to find the portion of the
ribbon used to type the evidence

14. Alterations of Documents - 1
Change after their original preparation
Erasures:
Trying to erase a part of a document
Disturbs the surface fibers of the paper (visible
under a microscope or under “side lighting”)
Obliterations
Trying to remove a part of a document chemically
Usually evident under a microscope. IR or UV
lighting usually shows where a document as been
altered this way

15. Alterations of Documents - 2
Adding to a document:
Can be exposed by shining a blue-green light on
the document. Many inks release differing
amounts of IR light in these situations. You can see
the difference in the inks.
Different inks also absorb IR light differently,
which can expose different inks
P 566 Figure 16-7
P567 Figure 16-8

16. Alterations of Documents - 3
Crossing things out or overwriting:
Usually not done because of its obviousness
Can hide the original writing if the inks are similar
enough
Analyzing charred documents:
Reflect light off of the document surface to
contrast the writing – p 569 Figure 16-10
Digitalizing is commonly done to investigate or
enhance documents - p 570 Figure 16-11 & p 571
Figure 16-12

17. Indented Writings
Partially visible indents on a piece of paper that
was underneath the written on paper.
These indents can contain incriminating
evidence, even if the original written document
can’t be found
Toner powder can be applied across a page to
find indented writings
P 572 Figure 16-3

18. Ink Comparisons
The composition of dyes can be compared by:
Visible microspectrophotometer
Thin-layer chromatography (TLC) – shows the dyes
broken into their components by how fast they
move up a column of paper
Can be compared to the US International Ink
Library
Describes not only type of dye but when it was
produced, etc

19. Paper Comparisons
Paper is usually made from cellulose fibers from
wood and fibers from recycled paper products
Can examine and compare:
Chemical makeup of paper
General appearance
Color
Weight
Watermarks
Read Forensics at Work p 558