Trace evidence

Forensic science laboratories are generally divided into separate specialty areas. These typically include forensic toxicology, soHd-dose dmg testing, forensic serology, trace evidence analysis, firearms and tool mark examination, questioned documents examination, and latent fingerprint examination. Laboratories principally employ chemists, biochemists, and biologists at various degree levels. In some specialty areas, eg, firearms examination, questioned... 

Trace Evidence. Trace evidence (23) refers to minute, sometimes microscopic material found during the examination of a crime scene or a victim s or suspect s clothing (see Trace AND residue analysis). Trace evidence often helps poHce investigators (24) develop connections between suspect and victim and the crime scene. The theory behind trace evidence was first articulated by a French forensic scientist the Locard Exchange Principle notes that it is not possible to enter a location, such as a room, without changing the environment. An individual brings trace materials into the area and takes trace materials away. The challenge to the forensic scientist is to locate, collect, preserve, and characterize the trace evidence. 

Searching a crime scene is a complex process (25), involving poHce, crime scene technicians, and forensic scientists. The procedure requires careful documentation, collection, and preservation of the evidence. Trace evidence (26) in criminal investigations typically consists of hairs (27,28) both natural and synthetic fibers (qv) (29,30), fabrics glass (qv) (31,32) plastics (33) sod plant material budding material such as cement (qv), paint (qv), stucco, wood (qv), etc (34), flammable fluid residues (35,36), eg, in arson investigations explosive residues, eg, from bombings (37,38) (see Explosives and propellents), and so on. 

Microscopy (qv) plays a key role in examining trace evidence owing to the small size of the evidence and a desire to use nondestmctive testing (qv) techniques whenever possible. Polarizing light microscopy (43,44) is a method of choice for crystalline materials. Microscopy and microchemical analysis techniques (45,46) work well on small samples, are relatively nondestmctive, and are fast. Evidence such as sod, minerals, synthetic fibers, explosive debris, foodstuff, cosmetics (qv), and the like, lend themselves to this technique as do comparison microscopy, refractive index, and density comparisons with known specimens. Other microscopic procedures involving infrared, visible, and ultraviolet spectroscopy (qv) also are used to examine many types of trace evidence. 

Microscopists in every technical field use the microscope to characterize, compare, and identify a wide variety of substances, eg, protozoa, bacteria, vimses, and plant and animal tissue, as well as minerals, building materials, ceramics, metals, abrasives, pigments, foods, dmgs, explosives, fibers, hairs, and even single atoms. In addition, microscopists help to solve production and process problems, control quaUty, and handle trouble-shooting problems and customer complaints. Microscopists also do basic research in instmmentation, new techniques, specimen preparation, and appHcations of microscopy. The areas of appHcation include forensic trace evidence, contamination analysis, art conservation and authentication, and asbestos control, among others. 

Criminalistics and trace evidence are both terms that apply to all types of physical material that may be circumstantial evidence in the trial of a case. Most often experts who are identified as criminalists, microanalysts, or trace evidence examiners analyze a variety of types of trace evidence. They carry out three types of identification. First is to determine the nature of small items of trace evidence. After this forensic experts compare the trace evidence with known materials for the purpose of determining the origin of the evidence. The third type of criminahstics investigations is performed in order to identify an individual to whom the trace belongs. For this purpose population studies using statistics (especially the probabilistic approach of Bayesian theory) and chemometrics methods are utilized. 

Microscopic techniques, 70 428 Microscopists, role of, 76 467 Microscopy, 76 464-509, See also Atomic force microscopy (AFM) Electron microscopy Light microscopy Microscopes Scanning electron microscopy (SEM) Transmission electron microscopy (TEM) acronyms related to, 76 506-507 atomic force, 76 499-501 atom probe, 76 503 cathodoluminescence, 76 484 confocal, 76 483-484 electron, 76 487-495 in examining trace evidence, 72 99 field emission, 76 503 field ion, 76 503 fluorescence, 76 483 near-held scanning optical,... 

See also SEM/EDS detectors used in, 24 78 development of, 16 487-488 electron sources used in, 24 77-78 in surface imaging, 24 75-76 silica, 22 371-372 for trace evidence, 12 100 Scanning probe microscopies, in surface and interface analysis, 24 80-84 Scanning probe microscopy (SPM), 16 466, 495-503... 

Trace analysis, of silicones, 22 599-600 Trace component analysis, for fats and fatty oils, 70 828 Trace elements analysis of, 25 370 silicone chemistry and, 22 549-550 Trace evidence, 72 99-102... 

Trace Evidence. Trace evidence refers to minute, sometimes microscopic material found during the examination of a crime scene or a victim s or suspect s clothing. Trace evidence often helps police investigators develop connections between suspect and victim and the crime scene. The challenge to the forensic scientist is to locate, collect, preserve, and characterize the (race evidence. 

Microscopy plays a key role in examining trace evidence owing to the small size of the evidence and a desire to use nondestructive testing techniques whenever possible. Polarizing light microscopy is a method of... 

In 1910 the French scientist Edmond Locard, inspired by the Adventures of Sherlock Holmes, postulated the fundamental principle on which forensic science and trace evidence is based, namely, The Locard Exchange Principle (Chisum and Turvey 2000). When two things come into contact, physical components can be exchanged. For example, the exchange can take the... 

Lombardi, G. (1999). The contribution of forensic geology and other trace evidence analysis to the investigation of the killing of Italian Prime Minister Aldo Moro. J. Forensic Sci. 44, 634-642. 

The major problem associated with trace evidence is the possibility of cross transfer to the suspect from some unrelated source. In Northern Ireland there must be a greater contamination risk than in the rest of the United Kingdom, due to the relative abundance of firearms and explosives. Cross-contamination allegations are a frequently used defense in court. Contamination risks have been exaggerated out of all proportion, and all problems in this area stem from the difficulty in providing basic facts, knowledge, and statistics... 

One of the problems with trace evidence is the possibility of contamination/ cross contamination. Contamination has already been mentioned in chapter 24 and contamination avoidance must be a priority. If it cannot be shown that contamination is unlikely to have occurred, then the significance of laboratory positive results will be substantially diminished. 

Dr. James Smyth Wallace is a retired U.K. forensic scientist and a 25-year veteran of the Northern Ireland Forensic Science Laboratory. He is the author/co-author of 14 scientific papers, as well as a forensic science textbook. He is a member of the Forensic Science Society and retains an active interest in forensic chemistry, particularly in the area of trace evidence detection. 

Also, as with Sal Palmer, there had been nothing found at the site to indicate who might have done this to her. The ground was baked too hard to yield footprints, and except for the rope fibres caught on her broken fingernails there was no trace evidence, no forensic clues left as to the killer s identity. 

A scientist in the trace-evidence section might have performed the physical analysis in the hit-and-run case men-... 

Hobbs J. R. and Conde E. P, A simple inexpensive thermal desorption method for the trace analysis of headspace vapors from explosives and organic nitro-Compounds, Proceedings of Interernational Symposium on Forensic Aspects Trace Evidence, FBI Quantico, VA, June 24-28, 1991, 269. Avail. NTIS PB94-145877. 

When possible, place on a clean sheet any victim to be transported. When the victim is transferred to the hospital bed, retain the sheet for law enforcement investigators to examine for trace evidence. 

Laser and inductively coupled plasma (ICP) emission spectroscopy constitute powerful multielement qualitative and quantitative tools for the analysis of metals, paints, and glass. Finally, ICP with mass spectrometry (MS) makes an increasing impact on the analyses of trace evidence from pollution source determination to traditional trace exploitation. 

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