Kris L. Sperry
Georgia Bureau of Investigation
Decatur, GA

Kim A. Collins
Medical University of South Carolina
Charleston, SC

Positive identification is of extreme importance in forensic pathology. Whether the body is one from a mass disaster, only a body part, a disposed neonate, or just an unknown decedent, identity must be accurate. In many cases, the external characteristics of an individual and reports by next-of-kin and/or acquaintances confirm the identification (a visual). However, in cases such as thermal injury, decomposition, mummification, mutilation, explosion, plane crash, and severe body trauma, positive identification can be quite challenging.

Types of Identification
Forensic identification is usually divided into presumptive and scientific identification categories. A visual ID takes into account facial features, race, sex, age, eye color, hair color, skin color, and any unique markings such as scars or tattoos. However, these characteristics can be influenced by time, emotion, and subjective evaluation of the next-of-kin or acquaintance. Other presumptive ID is based on where the body was found (home, car), clothing, and personal effects (wallet, personal papers). Anthropology studies of skeletal remains can determine the age, sex, race, stature, body (muscular) build, and certain diseases can be used to get a general idea of the physical make-up of the decedent. A forensic artist can take this information and sculpt a face of clay over the skull or construct a two dimensional drawing. Tissue depth markers are used to guide the artist in the placement of the clay or drawing of the features. The depths are based on the anthropology data. The end result is a likeness of the decedent. This reconstruction may not a true confirmation of identification, but the facial reconstruction will aid law enforcement in gathering information for positive scientific identification, such as dental and radiographic comparison (see below).

Scientific Identification
The science of fingerprints, dentistry, radiology, and DNA comparison are classified as scientific methods of identification.

Prints: Fingerprints are very reliable and have been used in the US since 1924. Fingerprints, palm prints, foot prints, and even lip prints are unique. No two are alike, even in identical twins. A fingerprint is made of a series of ridges and furrows on the surface of the finger. The uniqueness of a fingerprint can be determined by the pattern of ridges and furrows as well as the minutiae points. Minutiae points are local ridge characteristics that occur at either a ridge bifurcation or a ridge ending. Latent prints are impressions produced by the ridged skin on human fingers, palms, and soles of the feet. A print may be lifted from an individual and compared to a database. Of course, the issue is that the database must have a control for comparison. Unit examiners analyze and compare latent prints to known prints of individuals in an effort to make identifications or exclusions . In about 70% of cases received for comparison, a positive match can be made. In cases of fires, decomposition, or drowning, the epidermis and dermis may separate resulting in glove or stocking formation. The gloves and stockings can be printed for comparison with the database. On a mummified victim, the hand can even be soaked in glycerin to soften the skin and ridges and enhance the recovery of prints.

Dental: Dental comparison is an excellent means of identification when fingerprints or a visual identification can not be made. The jaws can be removed. Postmortem charting of the teeth and radiographs should be performed. A comparison can be made between premortem and postmortem dental x-rays/records and even casts. Restorations, prostheses, root structure, bone structure, presence/absence of teeth, and pre-existing disease characteristics are areas for comparison. For edentulous individuals, the jaw radiographs may still provide useful information. The premortem casts that were formed when making the denture can be used to compare with the decedent. Also, many dentures and prostheses now have the individual's name or social security number.

Radiography: Radiography can be used for scientific identification by comparing certain premortem and postmortem films. Besides the dental radiographs, frontal sinus patterns, old fractures, unique radiographic features, and certain foreign bodies/surgical devices can be the basis for comparison or radiographic superimposition. Any bone can be used for comparison.

DNA: Like print, dental, and radiographic identification, DNA identification needs a positive comparison between premortem and postmortem specimens. Good postmortem specimens are blood (10ml in an EDTA tube is preferred), blood filter spot, skeletal muscle, and spleen. Some laboratories will also use liver. If a body is decomposing(ed), femur bone marrow and molar tooth pulp can be procured. Because of the resistant nature of dental tissues to environmental assaults, such as incineration, immersion, trauma, mutilation and decomposition, teeth represent an excellent source of DNA material. Again, a known control must be available. Hair may yield mitochondrial DNA, a form of DNA that is passed through the maternal line. A decedent's next-of-kin may also provide DNA specimens (buccal scrapping) for comparison with the decedent's DNA specimen.

Several procedures can be performed in order to analyze DNA. Restriction Fragment Length Polymorphism (RFLP) analyzes the variable lengths of DNA fragments that result from digesting a DNA sample with a restriction endonuclease. The presence or absence of certain recognition sites in a DNA sample generates variable lengths of DNA fragments, which are separated using gel electrophoresis. They are then hybridized with DNA probes that bind to a complementary DNA sequence in the sample.

PCR Analysis (polymerase chain reaction) is used to make millions of exact copies of DNA from a biological sample. The ability of PCR to amplify small quantities of DNA enables even highly degraded samples to be analyzed. Great care, however, must be taken to prevent contamination with other biological materials during the identifying, collecting, and preserving of a sample.

STR Analysis, short tandem repeat, is used to evaluate specific regions (loci) within nuclear DNA. Variability in STR regions can be used to distinguish one DNA profile from another. The odds that two individuals will have the same 13-loci DNA profile are about one in one billion.

Mitochondrial DNA Analysis (mtDNA) can be used to examine the DNA extracted from mitochondria as opposed to nuclear DNA needed in RFLP, PCR, and STR. This is useful in older biological samples that lack nucleated cellular material. All mothers have the same mitochondrial DNA as their daughters. This is because the mitochondria of each new embryo come from the mother (ovum). The father's sperm contributes only nuclear DNA. Comparing the mtDNA profile of unidentified remains with the profile of a potential maternal relative can be an important technique in missing person investigations.

Y-Chromosome Analysis is especially useful for tracing relationships among males or for analyzing biological evidence involving multiple male contributors since the Y-chromosome is passed directly from fathers.

References

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2. Handbook of Forensic Pathology, 2^nd edition, College of American Pathologists, Northfield, Illinois, 2003.
   
   
3. Spitz, WU, editor. Medicolegal Investigation of Death, 3^rd ed. Charles C. Thomas, Springfield, Illinois, 1993.
   
   
4. DiMaio VJ, and DiMaio D. Forensic Pathology, 2^nd ed. CRC Press. New York 2001.
   
   
5. MacLean, Kogan, Stitt. Validation of Dental Radiographs for Human ID. Int Dent J 39(5):1195-1200.
   
   
6. Law C, Bowers CM. 1995. Radiographic Reconstruction of Root Morphology in Skeletonized Remains: A Case Study ASFO Manual of Forensic Odontology, 3rd Edition. Page 21-23.
   
   
7. Saukko, P and Knight, B, editors. Knight's Forensic Pathology, 3^rd ed. Arnold, London, 2004.
   
   
8. Fierro, MF, editor. College of American Pathologists Handbook for Postmortem Examination of Unidentified Remains, 2^nd ed. College of American Pathologists, Northifield, Illinois, 1998.