Full Unit 2 Notes

Impression Evidence

• An impression is made when one object makes physical contact with another, leaving some of its physical characteristics on the recipient.

• Soft or pliable materials leave three-dimensional impressions. Examples include putty, mud, concrete, and soft dirt.

• Hard surfaces have two-dimensional impressions. Examples include dirt, dust, blood, and ink.

• All impression evidence has a donor and a recipient.

• The donor contains some three-dimensional markings.

• Common donors include shoe soles and heels, tire treads, fingerprints, footprints, lip prints, tools, metal dies, and ribbing and texture in fabrics.

• The recipient is made of material that can form and hold a negative image of the donor markings.

• Common recipients include soft plastics, soil, putty, paint, dust, metals, plastics, and wood.

Significance of Impression Evidence

• The factor that determines if one object can be associated with another is the presence of unique characteristics in the donor.

• A three-dimensional pattern or marking must contain some characteristics that are unique to that object.

• The characteristics could have come about as an object is used or could be random.

• This type of evidence is valuable in associating a particular shoe or tire, for example, to a crime scene.

• Serial numbers can also be used, which are unique to an object.

• Not all impression evidence is unique.

• For example, a fabric pattern from denim jeans impressed in the paint of a car could have come from numerous pairs of jeans.

Footwear Impressions

• Footwear impressions may be left at crime scenes and in entry and exit locations of scenes.

• Footwear evidence may be overlooked because:

  • it may be nearly invisible

  • it may be on uneven ground

  • it may be trampled by other footwear

• Footwear evidence is misunderstood or undervalued by police, detectives, judges, and juries.

• Footwear evidence can be fragile—photography and casts should be made of the impressions.

• When footwear touches the ground:

  • A static electricity charge can be applied to the impression if the shoe is clean and dry.

  • This helps in the transfer of trace residues and dust to the impression.

  • The pressure exerted by the foot will cause the surface to deform and take on the contours of the surface of the footwear.

  • This may be permanent or temporary.

  • A mixture of static electricity and pressure help footwear to be impressed into a surface.

Types of Footwear Impressions

• There are positive and negative impressions.

• A positive impression is made because of the residue on the surface of the footwear that touches the surface. [4]

• This is the most common type of footwear impression.

• A negative impression forms if the shoe is clean, and the recipient surface contains a lot of dust or residue.

• Negative impressions result when someone tracks through blood, wet paint, or grease with clean shoes.

• A positive impression may be deposited after a negative impression if sufficient material is present.

• For example, if a person tracks through a liquid and leaves a negative impression (a shoe mark in the liquid), a positive impression made with the liquid of the shoe mark can also be left on a clean surface.

• An imprint is made when there is enough residue on the footwear to leave an impression on the recipient surface.

Information From Footwear Impressions

• If enough unique characteristics are present, the impression can be matched to the actual footwear that made the impression.

• Footwear impressions can provide information about:

  • the type, manufacturer, model, and exact size of the footwear

  • the route taken into and away from the crime scene

  • activities that took place during the crime

  • the number of people and suspects at the scene

  • characteristics of the gait of the wearer

Finding Footwear Impressions at the Crime Scene

• The first problem with footwear is finding it.

• Usually, entries and exits are examined.

• Finding footwear evidence may involve:

  • a systematic search that includes the route of entry and exit and the crime scene

  • utilization of strategies for detecting latent or invisible prints

  • oblique lighting and physical methods, similar to those used to detect fingerprint residues

  • a search that encompasses two- and three-dimensional impressions

Preserving Footwear Impressions

• Photograph footprints.

• Photograph the footprint with a ruler or measuring tool for court testimony.

• In two-dimensional footprint cases, a photo will be used for comparison.

• Three-dimensional footprints are casted using material that fills the impression and then hardens to capture the impression image.

General Treatment of Footwear Impressions at the Scene

• First, complete a visual record.

• Use digital still and video photography, classical film, and tape methods.

• This provides a record of the position of all footwear impressions and their general condition.

• Complete notes and sketches that document exact locations and circumstances.

• Take photographs that can be used for examining the individualizing characteristics.

• Take close-up photos with sufficient resolution and lighting.

• Second, determine how best to preserve and/or enhance the impression.

• Avoid altering an impression until examination-quality photographs have been taken.

• The impression and substrate should be removed and transported to the laboratory if possible.

• If removal is not practical:

  • a cast should be made if the impression is three-dimensional

  • it should be lifted if it is two-dimensional

Casting Footwear Impressions

• The primary material of choice to cast footprints is dental stone due to its hardness and ability to capture detail. [9]

• It captures detail of the footprint to a much greater extent than other materials, such as plaster of Paris. [9]

• Improved casting materials are drying faster and showing a great deal of detail. [9, 10]

• There are also several advantages of casting over photography: [9, 10]

• Photography requires a level, two-dimensional subject to be effective.

• This may be difficult to gain a proper perspective.

• Photography also makes it difficult to locate a measuring device and get a proper measurement of the size of the shoe that made the impression.

• Oblique lighting may obscure details in photographs.

• Casting was heavily used when photographic techniques were lacking, but then higher-resolution films decreased the use of casting of impressions. [9, 10]

• Presently, casting is making a bit of a comeback. [10]

• Plaster of Paris: [9]

• soft, even after drying

• made up of large particles that may cause the loss of crucial detail

• requires the use of forms and reinforcing materials

• Dental plasters and stones: [9]

• most commonly used

• more dense, uniform, smaller particle size

• quick drying and show more detail

Lifting Footwear Imprints

• Imprints in materials like dust or powder can be lifted using tape, as is done with fingerprints. [11]

• Gelatin materials also can be used for lifting such imprints. [11]

• The most popular technique involves the use of an electrostatic lifting device. [11]

• A large, static electricity charge will strongly attract dust and other fine powders. [11]

• The low-current, high-voltage charge is put across a film that attracts the particles from the impression, which is then a transferred image that can be photographed. [11]

• Impressions in grease, oil, blood, cushions, or carpeting materials may be impossible to lift. [12]

• Impressions made in materials that deform when impressed but then bounce back and lose the impression, like cushions and carpeting, can be lost when the substrate regains its shape, but residues embedded in the impression that forms an imprint may be lifted. [12]

Comparison of Footwear Impressions

• Footwear impressions can be individual evidence if there are sufficient, unique characteristics present. [12]

• There is no set number of unique characteristics necessary for a positive association to be made between an impression and a particular shoe. [12]

Tire Tread Impressions

• Tire tread is the part of the tire in contact with the road. [13]

• It serves to increase friction at the point of contact and minimize slippage. [13]

• Tires are mass-produced; there are few unique or individual characteristics. [13]

• With time and wear, tires pick up details that set them apart from other tires. [13]

Tire Impressions as Evidence

• More than two-thirds of major crimes in the U.S. involve an automobile. [14]

• Tire impressions are not recorded as often as they should be. [14]

• Crime investigators overlook this evidence. [14]

• Three major methods for recording tire impressions at a crime scene: [14]

• Photographs and drawings are the best methods of faithfully recording the overall scene.

• Tire impressions must be documented with photographs or casting quickly before weather factors destroy them.

Evidentiary Value of Tire Impressions

• Tire impression casts made with dental stone are much bulkier and harder to handle due to their size. [15]

• Three-dimensional casts make negative (opposite) impressions. [15]

• Document with photographs. [15]

• Use casting wax on tire impressions in snow. [15]

• Casts of tire treads can be made, examined, and compared.

• There are difficulties with tire tread impressions that are not seen with footwear, with size being the main issue.

• Casts should be taken of three-dimensional impressions.

• Tire impressions often cannot be taken up and moved to the laboratory.

• Several disadvantages of casting tire impressions that are not issues with footwear impressions:

• difficulty casting impressions on steep inclines

• tire impressions may be many feet long

• Negative impressions should never be compared to positive impressions.

• Casting materials are the same as those used with footwear impressions.

• Tire impressions can also assist in determining other information about the vehicle:

• Wheelbase may be determined (distance from the center of the front wheel hub to the center of the rear wheel hub).

• Stance may be determined (distance from the centerline of the right tire to the centerline of the left tire).

• Impressions are compared to inked treads of known vehicles for identification.

Collecting Tire Impressions

• Lifts can also be made of tire treads.

• Lifts of two-dimensional tire impressions are made in the same way as with footwear impressions.

• Several lifts of the same impression may be made in order to get the whole impression.

• Other data, including wheelbase and tire tread stance measurements, can be collected.

• This can be used to determine the make and model of a car or truck.

Serial Number Restoration

• Serial numbers are stamped into an object that is usually metal.

• When a serial number is stamped into metal, the crystal structure is affected.

• Metal is compressed, making it more dense than the surrounding metal, and the metal-to-metal bonds are disrupted, and the structure becomes weakened when a serial number is stamped into the surface.

• Filing or grinding may only eliminate enough metal to remove stamped numbers, but the altered metal underneath remains and can be used for restoration.

• Restoration involves polishing the surface with a fine abrasive and then slowly treating it with a corrosive acid.

• During the restoration process, the stamped metal will dissolve more quickly than the adjacent metal, and the serial number will be pressed into the metal once again.

• Different types of metals require different acids and conditions for restoration.

• It is extremely difficult to restore serial numbers in plastics.

• Plastics are treated differently than metals.

• Hydrochloric acid, water, and cupric chloride solution is a common means to recover serial numbers.

• Once the serial number is visible, it must be photographed, as it will fade from view with time.

• A camera should be used to take pictures of each number as it is restored.

Firearms Impressions Unit

• Firearms examination is complex, technical, and detailed work.

• Forensic firearms science encompasses the study of firearms.

• Firearms identification involves an analysis of marks on bullets or cartridge cases due to the mechanisms within the weapon.

• Forensic scientists who study firearms include the manufacture, operation and performance, the analysis of ammunition and its by-products, and the individualizing characteristics that are transferred from firearms to bullets and cartridge cases. These forensic scientists are firearms examiners.

• Firearm examiners:

• Identify bullets and cartridge cases—test fired evidence to crime scene evidence.

• Use tests to determine whether a weapon has been fired.

• Can estimate the distance of shooting incidents.

• Chemically restore obliterated serial numbers.

• Test items/people for gunshot residue (GSR).

• Analyze patterns of injury—wound ballistics.

  Types of firearms:

• Handguns, including revolvers and pistols.

• Shoulder firearms, including rifles, shotguns, machine guns, and submachine guns.

• The first thing done in firearm analysis is to make sure the firearm is checked for safety.

• A firearm is a durable piece of evidence that beyond forensic firearms examinations may be analyzed for latent prints, fiber and hairs. It should be photographed and documented and then secured for transport.

Rifling

• The interior surface of the barrels of firearms (except shotguns) are rifled.

• This creates “spin” of bullet as it emerges from the barrel.

• Spin creates angular momentum to the bullet, allowing it to achieve the desired trajectory.

• It consists of a series of lands and grooves.

Lands and Grooves

• Lands are the raised portions inside a firearm.

• Grooves are the lowered/indented portions inside a firearm.

• During manufacture, grooves are cut into the barrel by either large segmented tools, called broaches, or a rifling button, which is a stiff metal rod with a flanged tip.

• Grooves are cut in a spiral direction or twist.

• A barrel’s internal diameter is an exact measurement, caliber is an approximation.

• The caliber of American and British ammunition is typically measured in inches, and all others are measured in millimeters.

• Land impressions are striations pushed in on the bullet.

• Groove impressions are raised and smooth on the bullet.

Ammunition

• Ammunition is what a firearm fires. Typically, a self-contained cartridge is composed of one or more projectiles, propellant, and a primer.

• The two major types of ammunition are cartridges for handguns and rifles and shells for shotguns.

• Bullets can be classified as:

• lead

• fully jacketed

• semi-jacketed

How Ammunition Is Fired Through the Barrel

• The propellant continues to burn to limit friction between the bullet and rifling of the barrel after the hammer strikes the primer cap.

• Friction transfers lands and grooves and striations to the bullet’s exterior.

Gunshot Residue

• Hot gases and powder are discharged from a firearm when a bullet is discharged.

• This is known as gunshot residue (GSR).

• Elements in GSR:

• Barium

• Antimony

• Lead

Firearms Evidence

• Firearms evidence must be clearly documented and photographed.

• Portions of walls or items containing cartridges should be removed.

• Care must be taken not to mark or deface bullets or cartridges when collecting them—do not use metal tools!

• Bullets & cartridge casings should never be marked but put in a small vial or box and tagged.

Tool Mark Evidence

• Tool marks are defined as a scratch or other microscopic marking left by the action of a tool or an object.

• Impressed tool marks – when tools hit the surface at a perpendicular director.

• Striated tool marks – when tools hit the surface at a parallel direction.

• Tool marks can be individualized - tools wear with use and get scratched and nicked.

• The criterion of match of known and unknown tool marks is that there must be a significant number of similarities and no unexplainable differences.

• Virtually any tool can leave their markings.

Can Tool Mark and Firearm Evidence Be Unique?

• Yes, tool mark and firearm evidence can be unique.

Firearm Comparisons

• The comparison microscope is used for firearm comparisons.

Impression Evidence

• There is no minimum number of characteristics or points that need to be present in impression evidence for individualization.

• If there is sufficient, unique characteristics present, footwear impression can be individual evidence.

• There is no set number of unique characteristics necessary for a positive association to be made between impression and a particular shoe.

• Impression evidence may be overlooked due to:

• being nearly invisible

• being on uneven ground

• being trampled by other footwear

• Footwear evidence is misunderstood or undervalued by police, detectives, judges, and juries.

• Footwear evidence can be fragile—must use photography and make casts of impressions.

Searching for Impression Evidence

• Searches for footwear evidence may involve a systematic search that includes the route of entry and exit and the crime scene.

• Utilize strategies for the detection of latent or invisible prints.

• Oblique lighting and physical methods, similar to those used to detect fingerprint residues.

• The search should encompass two- and three-dimensional impressions.

2D and 3D Impressions

• Two-dimensional impressions are flat. Examples include dirt, dust, blood, and ink.

• Three-dimensional impressions have depth. Examples include putty, mud, concrete, and soft dirt.

Collecting and Documenting 2D and 3D Impression Evidence

• In two-dimensional footprint cases, a photo will be used for comparison.

• Three-dimensional footprints are casted using material that fills the impression and then hardens to capture the impression image.

Individualizing Impression Evidence

• The factor that determines if one object can be associated with another is the presence of unique characteristics in the donor.

• A three-dimensional pattern or marking must contain some characteristics that are unique to that object.

• The characteristics could have come about as an object is used or could be random in nature.

• This type of evidence is valuable in associating a particular shoe or tire, for example, to a crime scene.

• Serial numbers can also be used, which are unique to an object.

Restoring Serial Numbers

• When a serial number is stamped into metal, the crystal structure is affected.

• Restoration involves polishing the surface with a fine abrasive and then slowly treating it with a corrosive acid.

• It is extremely difficult to restore serial numbers in plastics.

• Metal is compressed, making it more dense than the surrounding metal, and the metal-to-metal bonds are disrupted, and the structure becomes weakened when a serial number is stamped into the surface.

• Filing or grinding may only eliminate enough metal to remove stamped numbers, but the altered metal underneath remains and can be used for restoration.

• During the restoration process, the stamped metal will dissolve more quickly than the adjacent metal, and the serial number will be pressed into the metal once again.

• A camera should be used to take pictures of each number as it is restored.

• Different types of metals require different acids and conditions for restoration.

• Plastics are treated differently than metals.

• Hydrochloric acid, water, and cupric chloride solution is a common means to recover serial numbers.

Questioned Documents: Definition and Examples

• A questioned document is defined as any object containing handwritten or printed material whose source or authenticity is in question.

• Questioned documents can appear on various materials, not limited to paper.

• Examples of questioned documents include:

  • Handwritten documents

  • Typewritten documents

  • Copied documents (xerography)

  • Computer-printed documents

  • Documents on multiple surfaces, such as painted surfaces, mirrors, and walls

Handwriting Analysis

Handwriting Exemplars

• Requested exemplars are writing samples taken from someone specifically for comparison with a questioned document.

• Advantages of requested exemplars:

• Control over content, paper, and writing instrument

• Ability to collect enough samples to minimize the chances of the writer disguising their writing

• Disadvantage of requested exemplars:

• If a significant amount of time has passed between when the questioned document was written and when the requested exemplar is collected, the handwriting may have changed.

• Non-requested exemplars are examples of a subject's writing taken during normal business or personal activities.

• Examples of non-requested exemplars:

• Checks

• Bills

• Diary entries

• Notes

• Advantage of non-requested exemplars:

• Samples are typically obtained from around the same time the questioned document was produced.

• Disadvantage of non-requested exemplars:

• Difficulty establishing the authenticity of the exemplar

Handwriting Comparisons

• The ability of a questioned document examiner to identify the author of a handwritten document depends on two factors:

• Sufficient individual characteristics must be present in the unknown sample.

• Sufficient samples of the alleged writer's authentic handwriting must be available.

• There is no set number of matching characteristics required for positive identification.

• The number of matches needed depends on:

  • Size of the questioned document and exemplar samples

  • Nature of the characteristics

  • Experience of the examiner

  • Using percentage probabilities to express findings is not permissible.

Characteristics Used in Handwriting Comparison

• Class and individual characteristics can be used for comparison.

• Common characteristics include:

  • Spacing between letters and words

  • Relative proportions of letters and within letters

  • Individual letter formations

  • Formations of letter combinations

  • Overall slant of the writing

  • Connecting strokes

  • Pen lifts

  • Beginning and ending strokes

  • Unusual flourishes

  • Pen pressure

Signatures

• A person's signature may not always represent their typical handwriting or contain the same individual characteristics. [5]

• A single signature may not be enough for a definitive conclusion. [5]

• Signatures tend to be sensitive to context. [5]

• Formal signature: Used on official documents and made carefully. [5]

• Informal signature: Used in routine correspondence. [5]

• Abbreviated or stylistic signature: Used for frequently signed items like checks and credit card receipts. [5]

• Signature exemplars should always be collected in context. [5]

Forged Signatures

• Signatures are common targets of forgery attempts. [6]

• Methods of forgery: [6]

• Practicing from a known sample

• Freehanding the signature

• Tracing

Characteristics of Forgery

• Common characteristics of forged signatures: [7]

• Lack of individuality

• Slow writing speed

• Unnatural appearance, resembling "drawing"

• Careful correction of mistakes

• Identical signatures (indicating tracing)

• Lack of rhythm

• Unnatural starts and stops

• Inconsistent letters

Disguised Writing

• Characteristics of disguised writing: [7]

• Inconsistent slant and letter formations

• Change in capital letters

• Use of block lettering

• Significant change in writing size

• Writing with the non-dominant hand

• Lack of rhythm

• Irregular spacing

• Unnatural starts and stops

• Excessive ornamentation

Printed Documents

Typewriters

• Examiners can determine if a document originated from a specific typewriter by examining: [8]

• Reproducible defects that develop as metal characters wear down, chip, bend, or misalign

• Determining the typewriter's make and model requires a comprehensive library of sample writings. [8]

Laser Printers and Copiers

• Characters used in xerography are unlikely to deform over time. [9]

• Individualization may be possible if recurring extraneous marks or toner blotches appear until the machine is cleaned. [10]

• Chemical analysis and comparison of toner samples can help identify the copier's make. [10]

Other Printed Documents

• Ink-Jet Printers: [11]

• Water-based ink sprayed onto paper

• Individualization may be possible through extraneous, reproducible markings and chemical analysis of ink.

• Fax Machines: [11]

• Individualization may be possible through extraneous markings, ink analysis, and the Transmitting Terminal Identifier (TTI).

Additional Examinations

• Document examiners also inspect document alterations, including: [12]

• Obliterations

• Erasures

• Added markings

• Indented writings

• Charred documents

• Analysis of inks, papers, and pencil leads is also conducted. [12]

• Examiners may be asked to determine the age of a document. [12]

Obliterations

• Obliteration: Overwriting existing writing or printing with another writing instrument. [13]

• Methods to reveal obliterated writing depend on the original writing and the obliteration method. [13]

• Examples of techniques: [13]

• Dissolving the obliteration

• Using a light source that penetrates only the obliteration

• Treating the paper with oil to change its refractive index

• Various soaking techniques

Erasures

• Abrasive erasure: Removing material with an abrasive eraser. [14]

• Easily detected due to disturbance of paper coatings and fibers. [14]

• Chemical erasure: Dissolving or bleaching ink. [14]

• Detectable by color variations in the paper or chemical behavior under different light sources. [14]

• Typewriter erasures: Using a ribbon to lift images from paper. [14]

• Visible as indentations detectable with oblique-angle photography and a low-power microscope. [14]

Indented Writings

• Indented writings: Images formed on underlying pages due to pressure on the top sheet of a pad. [15]

• Visualization methods: [15]

• Oblique lighting

• Electrostatic Detection Apparatus (ESDA), which uses toner to highlight indentations

Charred Documents

• Partially burned documents may still be decipherable.

• Ink or pencil may resist charring more than paper.

• Examination involves various light sources due to document fragility.

Training and Education of Questioned Document Examiners

• No formal college-based programs for questioned document analysis exist in the U.S.

• Training is primarily through apprenticeships, including:

• Formal coursework

• Study of relevant literature

• Apprenticeship under an experienced professional

• Legal aspects and mock trial exercises

• Certification is available through the American Board of Forensic Document Examiners.

Handling Questioned Documents

• Guidelines for handling questioned documents:

  • Avoid folding, cutting, tearing, marking, or writing on the document.

  • Do not use paperclips, staples, or hole punches.

  • Process fingerprints after document examination.

  • Transport by hand delivery or registered mail.

  • Maintain accurate chain of custody.

  • Photograph the document upon receipt.

  • Initial and date the document.

  • Store in a secure vault.

  • Minimize light exposure and handling.

  • Use transparent, plastic folders for storage.

  • Keep accurate records.

History of Fingerprints

• While there is evidence that ancient civilizations were aware of fingerprints, the first systematic use of fingerprint identification in the U.S. was in 1902 in New York City.

• The first U.S. criminal conviction using fingerprint evidence took place in 1904 in Chicago in the Thomas Jennings case.

• The FBI's Identification Division, established in 1924, became a national repository for fingerprint records.

What are Fingerprints?

• Fingerprints are the distinctive images created when a finger's ridges and furrows are pressed onto a surface.

• These friction ridges, found on the palms, soles, and finger and toe tips of all primates, evolved to enhance grip.

• Friction ridges develop in the uterus, starting around the 9th or 10th week of fetal development, and remain unchanged throughout life.

Types of Fingerprints

• Patent prints are visible without assistance because they are made with a transferable substance (e.g., blood, ink) or pressed into a soft material (e.g., clay).

• Plastic prints, a type of patent print, are three-dimensional impressions left in moldable materials.

• Latent prints, composed of sweat and oils, are invisible to the naked eye and require visualization techniques.

Finding Latent Prints

• Latent prints can be found using:

  • Alternative Light Sources: Many latent prints become visible under laser or black light.

  • Chemicals: Substances like iodine and ninhydrin react with amino acids in sweat, causing a color change.

  • Cyanoacrylate Fuming: Superglue fumes bind to proteins in fingerprint ridges, creating a white coating that can be further enhanced with powders or chemicals.

  • Powders: Colored, fluorescent, or magnetic powders are brushed lightly over surfaces, creating contrast to reveal the print.

Fingerprint Identification

• Sir Francis Galton was the first to study fingerprints scientifically and develop a classification system still used today.

• Friction ridges are considered unique, with an extremely low probability of two individuals having identical prints.

• Fingerprint identification relies on analyzing minutiae, the unique ridge characteristics (e.g., ridge endings, bifurcations) and their arrangement.

• The Henry Classification System, developed in the early 1900s, categorizes fingerprints based on pattern types (loops, arches, and whorls) for efficient database searching.

• Modern fingerprint identification relies on comparing minutiae and higher-level details.

• Automated Fingerprint Identification Systems (AFIS) are computerized databases used to store, search, and retrieve fingerprints.

Fingerprint Alteration

• While some attempts have been made to alter fingerprints, these modifications often make the prints easier to identify due to added scars and damage.