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Criminal Investigation

Learn about the science of fingerprint identification, classification methods, and lifting techniques used in criminal investigations. Discover the types of prints, chemical development processes, and the role of Automated Fingerprint Identification Systems (AFIS).

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Criminal Investigation

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  1. Criminal Investigation CJUS 201 Fingerprints Part 12

  2. Fingerprints • Friction ridge skin - hands: fingers, palms - feet: toes, soles, heels a. Side opposite fingernail: “bulb” - friction ridge outlines b. Two layers of skin - inner / outer (1) Epidermis

  3. Prints, cont. - contains ridges - 2 mm thick (2) Dermis - demal papillar - origination - scars / disease c. Uses (1) Friction ridges

  4. Prints, cont. - leaves impression - body secretions - material touched (2) Identification - permanent / individual - form on fetus (3) Hands / feet means to ID - fingers routinely used

  5. Prints, cont. • Prints - exact impression / image a. Most common means - perspiration - 99% water (1) Oils / chemicals - 1% amino acids / salts (2) Outside contaminants

  6. Prints, cont. b. Types of surface (1) Nonporous - most productive (2) Porous - chemical treatment (3) Plastic - photograph - cannot be developed

  7. Prints, cont. c. Impression - friction ridges - inside of fingers (1) Transferred - deposit of perspiration (2) Duplicated - by this - other substances

  8. Prints, cont. • Files maintained - sole purpose a. Arrest - WASIC - NCIC b. State requirements - employment - driver’s license - certificates

  9. Prints, cont. c. Professional license - health care - construction - accounting - education d. Military service - enlisted / civilian • Types of prints - visible / latent / plastic

  10. Types, cont. a. Latent prints - law enforcement - crime scene (1) Process - detecting / raising / lifting (2) Term - invisible - fingertips - secretions / contaminants

  11. Types, cont. b. Two sources of materials - natural / environmental (1) Natural - perspiration - body residue (acids / fats / salts) (2) Environmental - foreign matter - dust / soot / pollen / cooking oils

  12. Types, cont. c. Personal factors - print left or not (1) Physiology - perspire? (2) Surface type - suitable - unpainted wood / paper / textured - glass / enamel / metal / glossy

  13. Types, cont. (3) Pressure - firm / not heavy - ridges light - distort detail • Fingerprint classification - three primary patterns (types) a. Arch - ridges enter one side - rise / curve in center

  14. Classification, cont. - flow out opposite side (1) Plain / tinted (2) 5% – 10% b. Loop - enter on either side - make loop - flow out opposite side - same side

  15. Classification, cont. (1) Plain / double loop / central pocket loop / accidental (2) 60% - 65% c. Whorl - enter on both sides - form circle - flow out opposite side (1) 25% - 30%

  16. Classification, cont. • Fingerprint patterns - used to classify - not individualize a. Counted: core to delta - points of distinction - necessary for ID (1) France = 17 (2) England = 16

  17. Patterns, cont. (3) Spain = 10 to 12 (4) United States = 12 (5) Washington State = 12 b. Evidentiary value - crime scene - victim - person identified

  18. Patterns, cont. • Methods of classifying - mathematical formula - shapes / position / size a. Characteristics - unique properties in ridge detail - different from each other - different from one another b. Types - ending ridge

  19. Methods, cont. - bifurcation - dot - short ridge - island (enclosure) c. FBI: catalog of prints - NCIC (1) Taken in US (2) Vary: state to state

  20. Methods, cont. d. Collection: two purposes - evidence of patterns - positive identification • Lifting of fingerprints a. Dusting - specific steps (1) Brush is clean

  21. Lifting, cont. - roll handle (2) Shake powder - loosen (3) Apply lightly - follow contour lines (4) Remove excess (5) Photograph

  22. Lifting, cont. b. Lifting - commercial lift card (1) White / black background - color of powder - rubber lifter (2) Transparent tape - different sizes - palm size

  23. Lifting, cont. c. Transfer to card - identification • Chemical development - paper / cardboard / unpainted wood a. Iodine method - crystal fumes - absorbed by oils - yellowish/brown print (fade) - will fade / photograph immediately

  24. Development, cont. b. Ninhydrin - organic chemical - amino acids / protein (1) Kept 2 hours: room temperature - 1 to 3 days to fully develop (2) Purple-colored print - photograph immediately c. Silver nitrate

  25. Development, cont. - sodium chloride - perspiration - organic material (1) Reddish-brown - disappear 2 hours (2) Ultra-violet light - photograph immediately d. Cyanoacrylate fuming

  26. Development, cont. - esters / resins - “super glue” (1) Fuming chambers - vehicles - pads opened / placed (2) Non-porous surfaces - photographed - dusted - alter other biological evidence

  27. Development, cont. e. Radiation - raises prints (1) Ultraviolet rays - shows prints - dusted (2) Laser - vitamins in perspiration - skin / paper products

  28. Fingerprint Systems • AFIS - Automated Fingerprint Identification Sys. a. Technicians - digitize information - inkless prints - scanned - electronic image - stored in data base - access: NCIS / WASIC

  29. Systems, cont. b. Suspect print - classified (arch / loop / whorl / etc.) - 12 matching characteristics - data base computer (1) Produce comparisons - several matches - technician examines (2) Scan 1 million in 4.5 minutes

  30. Systems, cont. • Assessing surface - three types a. Non-Porous - glass / plastic / polished metal - finished wood / processes paper (1) Textured - photograph (2) Smooth

  31. Surface, cont. (3) Curvature b. Porous - paper / wood / some painted surfaces (1) Chemical - photograph (2) Fluoresce - photograph

  32. Surface, cont. c. Plastic - putty / plastics / adhesives - paint (semi-hardened) / plaster (1) Photograph • Rolling prints - from ‘V’ outward a. Right hand - thumb = 1

  33. Rolling, cont. - index = 2 - middle = 3 - ring = 4 - little = 5 b. Left hand - thumb = 6 - index = 7 - middle = 8 - ring = 9 - little = 10

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