FS Survey Quiz 7
o The collection of an adequate number of known writings (exemplars) is most critical for determining the outcome of a handwriting comparison.
Exemplar = an authentic sample used for comparison purposes • By "authentic" that means you know for certain who the source is. Examples: you watched the person create a known handwriting exemplar, you fingerprinted a person, you took a DNA sample directly from a person's mouth • Comparison disciplines require examiner to compare a questioned sample to a known sample to see if they "match". Exemplar is the known. It is critical to have the exemplar because without it you cannot do a comparison. (Caveat to the previous statement about questioned/knowns: can compare unknowns to see if they "match" each other - however you do not know the origin or source of the unknowns) Known writing should contain some of the words and combination of letters present in the questioned document and be adequate in number to show the range of natural variations in a suspect's writing. Natural variation = normal deviations found between repeated specimens of an individual's handwriting or any printing device • Ink and Paper Comparisons o A study of the chemical composition of the ink used on documents may verify whether or not known and questioned documents were prepared by the same pen; and the paper itself may be analyzed. Ink can be examines using instrumental analysis.
3 Fundamental Principles of Fingerprints
The three basic principles underlying the use of fingerprints in criminal investigations are that: • 1st : A fingerprint is an individual characteristic because no two fingers have yet been found to possess identical ridge characteristics o The acceptance of fingerprint evidence by the courts has always been predicated on the assumption that no two individuals have identical fingerprints o Supported by theoretical calculations: Researchers have devised mathematical models to determine the probability for the existence of two identical fingerprint patterns in the world's population - they conclude the probability is extremely small o Also supported by the fact that millions of individuals have had their prints classified over the past 120 years - no two have ever been found to be identical • 2nd : A fingerprint will remain unchanged during an individual's lifetime o The form and pattern of friction ridges is determined by the shape of the dermal papillae o Once the dermal papillae develop in the human fetus, the ridge patterns remain unchanged throughout life except to enlarge during growth o If an injury reaches deeply enough into the skin and damages the dermal papillae, a permanent scar will form. The presence of scars merely produces new unique characteristics for identification. • 3rd : Fingerprints have general ridge patterns that permit them to be systematically classified. o All fingerprints are divided into three classes on the basis of their general pattern: Loop = a class of fingerprints characterized by ridge lines that enter from one side of the pattern and curve around to exit from the same side of the pattern Whorl = a class of fingerprints that includes ridge patterns that are generally rounded or circular in shape and have two deltas Arch = a class of fingerprints characterized by ridge lines that enter the print from one side and flow out the other side
Analytical vs. Pattern Physical Evidence
• Analytical evidence = a laboratory-based analysis is used to examine this type of evidence o Chemical or serological tests o Instrumental analysis • Pattern evidence = an expert interprets or matches observed patterns (the patterns are the evidence) o Patterns/impressions are visually compared to each other to determine if they "match" o Patterns are interpreted to determine how they were created • Friction ridge evidence is pattern evidence because you are visually comparing friction ridge patterns from different sources to determine if they "match" (the pattern is the evidence)
Friction Ridge Analysis
• Friction ridge skin = the skin on the palmar surface of the hands and plantar surface of the feet that occurs in a corrugated fashion with elevated ridges broken up by lower furrows • Fingerprint = a reproduction of friction skin ridges found on the palm side of the fingers and thumbs • Ridge characteristics (minutiae) = ridge endings, bifurcations, and other ridge detail which must match in two fingerprints in order to find a common origin o There are as many as 150 minutiae on the average finger o The identity, number, and relative location of ridge characteristics impart individuality to a fingerprint o If two prints are to match, they must reveal characteristics that are not only identical but have the same relative location to one another in a print o Currently in the United States, there is no predetermined minimum number of friction ridge characters which must be present in two impressions in order to establish positive identification.
Comparison vs. Identification Analysis
• Identification = the process of determining a substance's physical or chemical identity o Ex: drug analysis, toxicology, species determination, explosive residue analysis o What is this object/substance? • Comparison = the process of ascertaining whether two or more objects have a common origin o Ex: Fingerprints, fiber comparisons, striations on bullets o Do two objects or patterns match? • Friction ridge analysis is a comparison discipline you are comparing an unknown friction ridge pattern found at a crime scene or on physical evidence to a known standard (from a person) or to other unknown friction ridge patterns to determine if they "match" or came from the same origin (person)
Individual vs. Class Characteristics
• Individual characteristics = properties of evidence that can be attributed to a common source with an extremely high degree of certainty o It is not possible to state with a mathematical exactness the probability that the specimens are of common origin. It can only be concluded that the probability is so high as to defy mathematical calculations or human comprehension. • Class characteristics = properties of evidence that can be associated with only a group and never a single source o Can never have a "match" using just class characteristics. Can only narrow it down to a group.
Types of Fingerprints: Latent, Visible, or Plastic Prints
• Latent print = a fingerprint made by the deposit of oils and/or perspiration; they are invisible to the naked eye o Once the finger touches a surface, body perspiration and/or oils present on the finger ridges are transferred to that surface, leaving an impression. • Visible print = a fingerprint made when the finger deposits a visible material such as ink, dirt, or blood onto a surface o Visible prints are made when fingers touch a surface after the ridges have been in contact with a colored material • Plastic print = a fingerprint impressed in a soft surface o Plastic prints are three-dimensional ridge impressions left on a soft material, such as putty, wax, soap, or dust.
Locating Fingerprints on evidence and at crime scenes
• Latent prints deposited on hard and nonabsorbent surfaces (e.g., glass, mirror, tile, and painted wood) are preferably developed by the application of a powder o Powders, available in a variety of colors, can be applied with a brush or magnetic wand, and adhere to perspiration and/or body oils of the print. o Super Glue® is approximately 98 to 99 percent cyanoacrylate ester, a chemical that actually interacts with and visualizes a latent fingerprint. Development occurs when fumes from the glue adhere to the print, usually producing a white latent print. • Latent prints on porous surfaces (e.g., papers, cardboard, and cloth) generally require treatment with a chemical o Examiners use various chemical methods to visualize latent prints on porous surfaces, such as iodine fuming, ninhydrin, and Physical Developer.
Other impressions made by the body
• Palm print = reproduction of the friction ridge skin on the palms • Handprint = impression of a hand • Footprint = impression of a foot • Lip print = the pattern of wrinkles on the lips (Cheiloscopy) • Bitemark impressions are in the pattern recognition category of analysis
Questioned Document Examination
• Questioned document = any document about which some issue has been raised or that is the subject of an investigation o Broad definition that covers all written and printed materials we normally encounter in our daily social and business activities: letters, checks, driver's licenses, contracts, wills, voter registrations, passports, petitions and lottery tickets o Not restricted to paper documents - may include writings or markings on walls, windows, doors, or any other objects • The uniqueness of handwriting makes this type of physical evidence one of the few definitive individual characteristics available. o Document experts continually testify to the fact that no two individuals write exactly alike. The unconscious handwriting of two different individuals can never be identical.
Comparing Impressions
• Same as with fingerprints - a comparison is done. A comparison is only possible when the item suspected of having made the impression is recovered o Need to make test impressions with known item to use to compare • Impressions will have both class and individual characteristics o Fingerprints Class: general ridge patterns Individual: minutiae (ridge charateristics) o Shoe prints Class: may be able to determine brand and shoe size Individual: unique and random gouges and marks o Tire tracks Class: may be able to determine brand and tire size (possibly narrow down type of vehicle) Individual: unique and random gouges and marks o Tool marks Class: possibly size or type tool Individual: unique and random gouges and marks
Impressions of other kinds:
• Shoe and footwear impressions • Tire track impressions • Fabric impressions: A pattern corresponding to the weave of fabric may be visible on surfaces • Tool mark = any impression, cut, gouge, or abrasion caused by a tool coming into contact with another object.
Individualization using ACE-V
• Using the ACE-V Process it is generally accepted that an examiner can use a fingerprint match to individualize a fingerprint to one person to the exclusion of all others • ACE-V = A four-step scientific method to identify and individualize a finger print o Analysis: The examiner assesses the unknown print to determine whether or not it is suitable for comparison. This involves the preliminary assessment of a number of factors like the surface material or, the substance of the print itself. o Comparison: compare the questioned print at (3) levels. Level 1: general ridge flow and pattern configuration Level 2: locating and comparing ridge characteristics (minutiae) Level 3: examination and location of ridge pores, breaks, creases, scars and other permanent minutiae o Evaluation: The examiner answers a few questions then it requires one of three decisions to be arrived at: Identification = the latent print and exemplar came from the same source Exclusion = the latent print and exemplar did not come from the same source Inconclusive = one cannot determine that the latent print and exemplar came from the same source, or not, to a sufficiently strong level of certainty o Verification: examiner's conclusion is confirmed by a second examiner. Requires an independent examination of the questioned and known prints by a second examiner A consensus must be arrived at by both examiners
