Forensic Science

4th AmendmentThe 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.

The Document ExaminerUsually 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 characteristicsThe uniqueness of handwriting can be

considered individualized evidence

Comparing Handwriting – General StyleFirst learning to write involves copying a

style from a teacherPage 556 Figure 16-1At this early stage handwriting of different

students is very similarAs a person grows up they start personalizing

their handwriting styles without even thinking about it

Comparing Handwriting - VariationsVariations 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

Challenges to Comparing HandwritingThe 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 characteristicsFrequently done with threatening letters, etc

When there is enough writing for comparison, the attempt to hide individualizing characteristics may failPage 557 Figure 16-2

Collecting Writing SamplesWriting 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 evidenceEx: can’t compare writing from when a suspect was

12 to when he was 20

Getting an Accurate ExemplarThe 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)

Comparing Typescript DocumentsThe 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

Comparing Photocopied DocumentsComparisons usually involve looking at defect

marks made by debris on the glass surface, inner cover or mechanical portions of a copier

Comparing Faxed DocumentsMost important to study and compare the

header (Transmitting Terminal Identifier)P 562 Figure 16-4Can be faked, but microscopic examination

usually reveals the falsity Can use the header to determine the machine’s

model

Comparing Computer Printed DocumentsWhen 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 microscopeFind the chemical compounds within a tonerFind the type of paper usedThe method used to apply the toner to the paper

EX: ink-jet, thermal transfer, laser printers, etc

Comparing Typewritten DocumentsFinding 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 identicallyFull 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

Alterations of Documents - 1Change after their original preparationErasures:

Trying to erase a part of a documentDisturbs 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

Alterations of Documents - 2Adding 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

Alterations of Documents - 3Crossing things out or overwriting:

Usually not done because of its obviousnessCan hide the original writing if the inks are

similar enoughAnalyzing 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

Indented WritingsPartially 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 writingsP 572 Figure 16-3

Ink ComparisonsThe composition of dyes can be compared by:

Visible microspectrophotometerThin-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

Paper ComparisonsPaper is usually made from cellulose fibers

from wood and fibers from recycled paper products

Can examine and compare:Chemical makeup of paperGeneral appearanceColorWeightWatermarks

Read Forensics at Work p 558