crime scene fingerprints
DESCRIPTION
“Regrets are as personal as fingerprints.” - Margaret C. Banning. Crime Scene Fingerprints. v isible prints r idges in contact with a colored material b lood, paint, grease, ink p lastic prints r idge impressions left on soft material p utty, wax, soap, dust l atent prints (invisible) - PowerPoint PPT PresentationTRANSCRIPT
CRIME SCENE FINGERPRINTS
“Regrets are as personal as fingerprints.”- Margaret C. Banning
WHAT TYPES CAN YOU LEAVE? visible prints
ridges in contact with a colored material blood, paint, grease, ink
plastic prints ridge impressions left on soft material
putty, wax, soap, dust
latent prints (invisible) ridge impressions left by oils and perspiration
VISIBLE PRINTS
PLASTIC PRINTS
LATENT PRINTS
LOCATING AND DEVELOPING PRINTS The type of surface
determines how to make them visible hard, nonabsorbent
surfaces (glass, mirror, tile, painted wood)
soft, porous surfaces (papers, cardboard, cloth)
Most difficult aspect may be just locating the prints
Latest technology – RUVIS (reflected UV imaging system)
Can locate prints on nonabsorbent material without aid of powders or chemicals
FINGERPRINT POWDERS work best on nonabsorbent surfaces variety of composition and colors when applied lightly with camel-hair or fiberglass
brush, will adhere to residue of sweat and/or oils left on surface
choose color that contrasts with background best magnetic powder (less chance that print will become
damaged or destroyed) – useful on surfaces like leather or rough plastics (textures could hold onto too much regular powder)
fluorescent powders used to obscure backgrounds
IODINE FUMING solid crystal that sublimates iodine vapors combine with oils (or may
interact with residual water left on a print)
not permanent, begin to fade once fuming is stopped – should photograph ASAP
WHILE WE ARE FUMING… Superglue (cyanoacrylate) fuming as
well Fumes adhere to patent print, usually
producing a white pattern – still only on nonporous surfaces
Can use any small, enclosed area – even a car’s interior!
(movie scenes)
WHAT ABOUT POROUS SURFACES? ninhydrin – (triketohydrindene hydrate)
usually sprayed onto surface with aerosol can reacts with amino acids in perspiration solution prepared by mixing with solvent like
acetone or ethanol (0.6% solution is most effective)
prints begin to appear within an hour or two – can be sped up if treated in oven or hotplate
has developed latent prints on paper as old as 15 years
PHYSICAL DEVELOPER (YES, THAT’S ITS NAME…)
silver nitrate based liquid reagent detects prints that iodine and ninhydrin
may have missed also effective on porous surfaces that may
have been wet at one time application will wash away any traces of
proteins from an object's surface protocol – iodine first, then ninhydrin,
then PD
AFTER ALL THIS, WE WANT TO PRESERVE THEM!
digital imaging picture converted into pixels, can be
enlarged for analysis photographs fingerprint tape
lifting print off surface, can be transferred to card for later study/scanning