1 forensic science chapter 16: document and voice examination

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Forensic Science

Chapter 16: Document and Voice Examination

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Questioned Document

• Any document about which some issue has been raised or that is the subject or an investigation• source or authenticity is in doubt

• May include writings on walls or other objects

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QD success

• Based on applying knowledge gathered through years of experience and training.

• Comparison-based• Need known writings

• As unique as fingerprints

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General style

• Learned in school as we copy letters• For young learners, handwriting is

very similar.• Changes by time and locale• As the learner gets better at writing

and the process becomes subconscious, they start to develop their own style and writing becomes more unique.

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Variations• Expected in

• Slope• Speed• Pressure• Letter and word spacing• Relative sizes of letters• Connections• Pen movements• Writing skill• Finger dexterity

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Variations from habits

• Margins• Spacings• Crowding• Insertions• alignment

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Other variations

• Spelling• Punctuation• Phraseology• grammar

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comparisons

• Must be based on many characteristics

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Difficulties

• Only a few words• Written to disguise

• Threatening letters• Attempt may fail if the document is

long

• Altered by drugs or alcohol

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Exemplar

• An authentic sample used for comparisons purposes

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Natural Variations

• Normal deviations found between repeated specimens of an individual’s handwriting or any printing device.

• Handwriting changes with age (but slowly)

• If a signature matches exactly, that points towards forgery by tracing.

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Getting exemplars

• May be obtained by court order• Handwriting samples are not

protected by the fifth amendment• Right to not incriminate yourself

• Doesn’t violate the fourth amendment• Police need a warrant to search you

or your property

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Getting a good sample

• Let the writer sit comfortably without distraction.

• Don’t show them the QD or help them with spelling or punctuation.

• Use similar pen and paper to the QD.

• Use the same words as the QD

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Getting a good sample

• Don’t tell them when to use uppercase unless necessary.

• Collect at least a page of exemplar.• Have them repeat the writing three

times.• Have them write signatures with

other text – such as a check.• Have the QD examined before

taking exemplars.

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Comparing typewriters

• Determine make and model• databases

• Compare to suspect machine• Wear and tear

• Letters are too high or low• Letters are off to one side• Letters slant

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Comparing printers, copiers, and faxes• Make and model• Compare with suspect machine

• Markings produced by machine• Debris in machine

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Erasure

• The removal of writings, typewriting, or printing from a document.

• Either chemical means or an abrasive instrument.

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Erasures

• Upper fibers are disturbed.• Can be see with a microscope or

oblique (side) lighting.• Can’t always determine what was

erased.

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Infrared luminescence

• Some dyes emit infrared light when exposed to blue-green light.

• Used to detect alterations made with a different kind of ink.

• Used to reveal writing that has been erased.

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Obliteration

• The blotting out or smearing over of writing or printing to make it unreadable.

• Difficult to recover if the same ink is used.

• Different inks may be detected using infrared photography.

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Charred document

• Has become darkened and brittle through exposure to fire or excessive heat.

• Can decipher using infrared photography or light at different angles.

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Digitizing

• Storing an image into a computer’s memory.• Scanner• Digital camera

• Digitized images can be edited using a program such as Adobe Photoshop ®• Lighten/darken• Color• Contrast• See color plates between pages 478 and 479

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Indented writings

• Impressions left on papers positioned under a piece of paper that has been written on.

• Readable under oblique lighting• Electrostatic detection

• The paper is charged and toner is applied.

• The toner sticks to the indented writings, making them visible.

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Ink analysis

• Chromatography is used to separate ink into individual dyes.

• The Treasury Department is compiling a database of inks.

• Can prove backdating if the dye used was not yet available.

• Tagged ink – produced using a different chemical tag each year to allow precise dating.

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Paper analysis

• General appearance• Weight• Color• Watermarks• Fiber identification• Additives, fillers, and pigments

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Chromatography

• More notes coming soon…..

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Sound spectrograph

• Converts speech into a visible graphic display

• developed in 1941 at Bell Telephone Laboratories

• Used during WWII• Now widely accepted as evidence

in court

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Voiceprint

• Pictorial representation of the frequency, duration, and amplitude of human voice sounds

• Used for identification

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Body parts involved in speech• Brain

• Controls speech process

• Lower respiratory Tract• Trachea, lungs, diaphragm• Used to supply the breath stream

• Vocal cords• Used to modulate breath stream

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• Vocal Cavities• Nasal (nose), oral (mouth),

pharyngeal (throat)• Used to select and suppress

overtones

• Articulators• Lips, teeth, tongue, jaw, soft palate• Used to vary the vocal cavities

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Spectrogram (voiceprint)

• Frequencies are converted into electrical energy and recorded on special paper.

• Shows• Time (horizontal axis)• Frequency or pitch (vertical axis)• Intensity or loudness (darkness)

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Computerized voiceprints

• Easier analysis• Allows high quality playback

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Categories of identification

1. Positive identification – more than 20 matching speech sounds

2. Probable identification – more than 15 matching sounds and no unexplained differences

3. Possible identification – more than 10 matching sounds and no unexplained differences

4. Inconclusive decision – usually from poor recording

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5. Possible elimination – 10 or more sounds that do not match

6. Probable elimination – 15 or more sounds that do not match

7. Positive elimination – 20 or more sounds that do not match