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How are fingerprints used in Forensics?

How are fingerprints used in Forensics?

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How are fingerprints used in Forensics?

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  1. How are fingerprints used in Forensics? Fingerprints are impressions that are left on surfaces in the oil which is deposited by a persons touch. Every living person has a unique pattern of ridges and depressions on the tips of their fingers. This makes it possible to positively identify an individual victim or criminal or prove the presence of a suspect at a crime scene.

  2. History • The principle of fingerprint was recognized three thousand years ago in ancient China, where it was common for legal contracts to be endorsed by the fingerprints of the parties involved. • This custom was also adopted by the Japanese. • In the 1900’s, William Herschel introduced contracts “signed” by the print of the signatory’s right hand. • First group to use computer stored fingerprint records was the Royal Canadian Mounted Police in the mid-1970’s. • Finger print records can now be scanned at tens of thousands of prints per second.

  3. Collection • Fingerprints found at a crime scene fall into three main categories: • Visible • Easiest to spot • Made by fingers that have been in contact with paint, ink, blood, etc… • Plastic • Made by fingers pressing into a soft surface • Latent • Most common & hardest to see • Made when natural oils & perspiration are transferred to a surface by touch • Magnetic powders and tape • Dust them with a powder. • White powder is used on dark surfaces. • Dark powder is used on light-colored surfaces. • Ninhydrin spray turns purple in contact with human amino acids. • Silver nitrate reacts with salt in perspiration forming silver chloride and is revealed under UV light. • Fuming with super-glue relies on cyanoacrylate ester. • Fuming with iodine for lifting prints from fabrics.

  4. Categorization • Patterns of ridges on the surface. • Three basic types of fingerprints: • Loops (2/3’rds of population have loops) • Radial • Ulnar • Ridges/Arches • Plain • Tented • Whorls (almost 1/3’rd of population has whorls) • Plain • Double Loop • Central Pocket Loop • Accidental

  5. Comparison • Visual identification • Computer recognition (American Fingerprint Identification System AFIS)

  6. Reliability • No two persons have the same patterns of ridges and depressions. • With a high quality print and a known set of prints for comparison, such as a victim or AFIS data base, positive ID of a body, suspect, or individual’s presence at a crime scene is possible. • Without a known set for comparison, fingerprints can provide direction for an investigation.

  7. Additional Applications for Using Fingerprints • Child-find kits • Pre-employment background checks • Security clearance • Secure accessibility for door entrances, computers, etc…

  8. Resources • Hidden Evidence by David Owen, Firefly Books, 2003, pp. 160-167 • Crime Scene Investigations by Pam Walker & Elaine Wood, The Center for Applied Research in Education, 1999, pp. 3-10 • Poster - “Fingerprint Classification Chart” Ward’s Natural Science – designed by Robert Verni •