Unformatted text preview: Fingerprints
Introduction to Forensic Science Individualization What kind of characteristics are required in order for physical evidence to be capable of positive identification? What proof is there for the uniqueness of fingerprints? Fingerprints are the result of contact of the fingers with a surface Friction ridges are responsible for the unique patterns Positive vs. negative Minutia What are they? Historical Bankground Recognition of ridge detailChinese (?) 3k yrs ago Anthropometry and Alphonse Bertillon mid 19th century Sir William Herschel – 50 yr. study in India Henry Faulds – uniqueness; first to publish Sir Francis Galton – Finger Prints (1st text); got British to adopt as adjunct to Bert. System Bertillon’s downfall – West vs. West Juan Vucetich – Argentine/South America: classification 1891 Sir Edward Henry classification system (to 100K) Fingerprint Card Plastic Print Patent Print Latent Print Before Enhancement After Enhancement Principle #1
A Fingerprint is an Individual Characteristic How do we know that? Galton’s calculation said 64 billion different possible combinations Later experts have attempted to devise other mathematical models Bottom line – infinitesimally small probability of duplicating DNA & FPs 90 years of classifying has failed to produce duplicates How are fingerprints compared? Point by point comparison Charted Principle #2
A Fingerprint will remain unchanged for life Origin of Residue Principle #3
Fingerprints have general patterns that permit classification Basic Patterns Whorl Loop Arch 6065% of population has loops 3035% has whorls 5% has arches 10 print classification Requires all 10 prints of suspect and at crime scene Subcategories of the 3 main patterns Loop – 1 or more ridges enter & exit from same side if loop opens toward little finger it is ulnar loop if loop opens toward thumb it is radial loop type lines: 2 diverging lines that surround pattern delta: at point of divergence core: center of pattern Whorls – 4 distinct groups: plain, central pocket, double loop, accidental (all must have type lines and at least 2 deltas) If a line is drawn between 2 deltas and it touches any spiral ridge, it is a plain whorl; if not, it is a central pocket loop whorl pattern Double loop – 2 loops combined Accidental – 2 or more patterns combined or other Arches: plain; tented (do not have type lines, deltas or cores) Classifying prints Henry System: 10 prints required; series of numbers & letters; 100K max FBI System: Several divisions involved Primary classification of FBI System: part of original Henry system; 1,024 groups that include all fp cards R. Index/R. Thumb R. Ring/R. Middle L. Thumb/R. Little L. Middle/L. Index L. Little/L. Ring Fingers are paired in a sequence Whorl pattern is basis: 16, 8, 4, 2, 1 (if on either finger) Loop or arch has a value of 0 The numerators are added + 1 and the denominators added + 1 to yield a primary classification fraction About 25 % of the pop. is 1/1 (all loops and/or arches) What does classification do? Does not identify a person (class characteristics) Identification requires side by side ridge comparison (individual characteristics) 10 prints required Some agencies have single print files (only useful for specific crimes/criminals) AFIS/IAFIS Scans and digitizes images based on ridge endings and bifurcations Determines degree of correlation 10 print vs. single print search How automated is it? Cold hits (S.F. 18 v. 8 manually) Almost Heaven, WVA What constitutes identification? Numbers of “points” required – 8 to 16 IAI 3 yr study (1973) 1995 international conference reaffirmed Bottom line – it is about more than points Methods of detecting Visible/plastic (patent) Latent Special lighting: laser, forensic light source, RUVIS Physical vs. chemical: What would a drop of water do on the surface? What is a fingerprint comprised of? Perspiration: water, salt, protein material Oil (from touching hairy areas – not from pores) Physical Enhancement Physical Enhancement Laserinduced Fluorescence Physical Enhancement Enhancement Methods Chemical Chemical Enhancement Special Methods Sticky side powder Bloody Prints Criteria for Identification Dallas P.D. vs. FBI vs. Scotland Yard SWGs Darlie Daubert vs. Dow Pharmaceutical Madrid fiasco Baltimore County ruling FINIS ...
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- Spring '11
- Characteristic, Physical Enhancement, central pocket loop, type lines, surface Friction ridges, Edward Henry classification