1. What is a Fingerprint?

2. A Fingerprint is: A deposit of:
98% perspiration
1% amino acids
1% oils
Formed on the friction ridges of fingers, palms & feet
These materials are left on the surface contacted

3. Inorganic Constituents of fingerprint residue from sweat
Major Components
Na+ K+
Ca2+
Fe2+
Cl- F-
Br- I-
HCO3-
PO43-
SO42-
NH4OH

4. Inorganic Constituents of fingerprint residue from sweat
Minor Components
Mg2+
Zn2+
Cu2+
Co2+
Pb2+
Mn2+

5. Organic Constituents of fingerprint residue from sweat
Proteins
Amino Acids
Lipids
Glucose
Lactate
Urea
Pyruvate
Creatine
Creatinine
Glycogen
Uric Acid
Vitamin Sterols

6. Skin Cross Section

7. Types of Fingerprints Left at the Crime Scene
Latent print impressions
Patent print impressions
Plastic print impressions
Katent print impressions

8. Patent Print Readily visible to the naked eye
Usually the result of some substance coating the ridge detail and then allows the transfer transfer of ridge detail to a surface that is touched.
More common substances at a crime scene:
Blood, paint, grease
Photograph to preserve as evidence

9. Plastic Prints
Visible print to the naked eye where the print detail is usually in a soft surface
More common surfaces/substances seen at a crime scene:
Window putty, dust, dirt, mud
Photograph to preserve as evidence

10. Katent Prints Prints made by pre-puberty children
Minutia more compact than adult
Not made by sweat remnants
Easy to lose on objects because mainly composed of water

11. Latent Prints Prints not visible to the naked eye
Prints need to be made visible
through:powders, chemical processes, or lasers
Most common type of impressions left at crime scenes.

12. Non-destructive Methods of Lifting Prints
Visual exams
Alternate light source (ALS)
Photography

13. Destructive Methods of Lifting Prints
Physical Means (better for non-porous):
Conventional Powders, Magnetic Powders, Fluorescent Powders
Chemical Means (better for porous materials):
Ninhydrin, Silver nitrate, Superglue (Cyanoacrylate ester), Iodine fuming, Physical Developer (PD), 1,8-diazafluorenone (DFO)

14. What to include on lift card
At a minimum include:
Case #
Date
Print #/letter
Initials of lifting technician

15. Practice lifting using conventional powder after being shown the technique using a slide

16. Practice lifting using magnetic powder after being shown the technique using a slide

17. Chemical Lifting Techniques
Use with porous objects

18. Iodine Not really a chemical reaction Temporary
Place a few crystals in closed container with object.
Iodine sublimates
Photograph print to preserve it

19. AgNO3(aq) Cover area with solution (we will use a brush)
Expose area to high energy (e.g. UV) light source (be careful not to overexpose print)
Photograph to help preserve
AgNO3(aq) reacts w/ salts that are present
AgNO3(aq) + Cl-  AgCl- + UV  2AgCl
2Ag0 +Cl20

20. Ninhydrin
Ninhydrin dissolved in alcohol (ethyl, isopropyl, methyl, or butyl alcohol)
Reacts w/ amino acids in print (forms Ruhemann Purple)
Place object in solution (or spray solution on large object, wear protection) to soak
Allow object to dry (warm & humid area best)
Iron object with steam setting (introduces warmth & humidity)

21. Ninhydrin reaction
Ruhemann Purple

22. Sample results for Ninhydrin

23. 2 more photographic processes
1-8, diazafluoren-9-one (DFO)
Physical Developer (PD)
Both react with salts that are left in the prints
Used more often than AgNO3(aq) but similar processes

24. Gentian violet (crystal violet)
Stains fats/oils left behind
To make solution- .02g/80mL dH2O
Used for finding prints on “sticky” side of tape
Place tape piece in solution
Rinse tape with water
Photograph prints that are present

25. Super Glue (Cyanoacrylic Esters)
Uses polymerization
Developed prints appear white
Heat process:
Place control print in developing area
Place 2-3 drops/gal of container on dish
Heat (we will use coffee warmer)
NaOH method:
Place ~10 drops on cotton ball containing NaOH