<CHAP NUM="3" ID="CH.00.003"><FM><TTL>Physical Evidence</TTL>
<KTSET><TTL>Key Terms</TTL>
<KT>class characteristics</KT>
<KT>comparison</KT>
<KT>identification</KT>
<KT>individual characteristics</KT>
<KT>product rule</KT>
<KT>reconstruction</KT></KTSET>
<OBJSET><TTL>Learning Objectives</TTL>
<P>After studying this chapter you should be able to:
<OBJ><P><INST>< </INST>Review the common types of physical evidence encountered at crime scenes</P></OBJ>
<OBJ><P><INST>< </INST>Explain the difference between the identification and comparison of physical evidence</P></OBJ>
<OBJ><P><INST>< </INST>Define and contrast individual and class characteristics of physical evidence</P></OBJ>
<OBJ><P><INST>< </INST>Appreciate the value of class evidence as it relates to a criminal investigation</P></OBJ>
<OBJ><P><INST>< </INST>List and explain the function of national databases available to forensic scientists</P></OBJ>
<OBJ><P><INST>< </INST>Explain the purpose physical evidence plays in reconstructing the events surrounding the commission of a crime</P></OBJ></P></OBJSET>
<CASE TY="CS"><TTL>The Green River Killer</TTL>
<P>This case takes its name from the Green River, which flows through Washington State and empties into Puget Sound in Seattle. In 1982, within six months the bodies of five females were discovered in or near the river. The majority of the victims were known prostitutes who were strangled and apparently raped. As police focused their attention on an area known as Sea-Tac Strip, a haven for prostitutes, girls mysteriously disappeared with increasing frequency. By the end of 1986, the body count in the Seattle region rose to forty, all of whom were believed to have been murdered by the Green River Killer. As the investigation pressed on into 1987, the police renewed their interest in one suspect, Gary Ridgway, a local truck painter. Ridgway had been known to frequent the Sea-Tac Strip. Interestingly, in 1984 Ridgway had actually passed a lie detector test. Now with a search warrant in hand, police searched the Ridgway residence and also obtained hair and saliva samples from Ridgway. Again, insufficient evidence caused Ridgway to be released from custody. With the exception of one killing in 1998, the murder spree stopped in 1990, and the case remained dormant for nearly ten years. But the advent of DNA testing brought renewed vigor to the investigation. In 2001, semen samples collected from three early victims of the Green River Killer were compared to Ridgway’s saliva that had been collected in 1987. The DNA profiles matched and the police had their man. An added forensic link to Ridgway was made by the location of minute amounts of spray paint on the clothing of six victims that compared to paints collected from Ridgway’s workplace. Ridgway avoided the death penalty by confessing to the murders of forty-eight women.</P></CASE></FM>
<BM><P>It would be impossible to list all the objects that could conceivably be of importance to a crime; every crime scene obviously has to be treated on an individual basis, having its own peculiar history, circumstances, and problems. It is practical, however, to list items whose scientific examination is likely to yield significant results in ascertaining the nature and circumstances of a crime. The investigator who is thoroughly familiar with the recognition, collection, and analysis of these items, as well as with laboratory procedures and capabilities, can make logical decisions when the uncommon and unexpected are encountered at the crime scene. Just as important, a qualified evidence collector cannot rely on collection procedures memorized from a pamphlet but must be able to make innovative, on-the-spot decisions at the crime scene.</P>
<H1>Common Types of Physical Evidence</H1>
<NL><ITEM><TTL><INST>1. </INST>Blood, semen, and saliva.<INST> </INST></TTL><P>All suspected blood, semen, or saliva—liquid or dried, animal or human—present in a form to suggest a relation to the offense or people involved in a crime. This category includes blood or semen dried onto fabrics or other objects, as well as cigarette butts that may contain saliva residues. These substances are subjected to serological and biochemical analysis to determine identity and possible origin.</P></ITEM>
<ITEM><TTL><INST>2. </INST>Documents.<INST> </INST></TTL><P>Any handwriting and typewriting submitted so that authenticity or source can be determined. Related items include paper, ink, indented writings, obliterations, and burned or charred documents.</P></ITEM>
<ITEM><TTL><INST>3. </INST>Drugs.<INST> </INST></TTL><P>Any substance seized in violation of laws regulating the sale, manufacture, distribution, and use of drugs.</P></ITEM>
<ITEM><TTL><INST>4. </INST>Explosives.<INST> </INST></TTL><P>Any device containing an explosive charge, as well as all objects removed from the scene of an explosion that are suspected to contain the residues of an explosive.</P></ITEM>
<ITEM><TTL><INST>5. </INST>Fibers.<INST> </INST></TTL><P>Any natural or synthetic fiber whose transfer may be useful in establishing a relationship between objects and/or people.</P></ITEM>
<ITEM><TTL><INST>6. </INST>Fingerprints.<INST> </INST></TTL><P>All prints of this nature, latent and visible.</P></ITEM>
<ITEM><TTL><INST>7. </INST>Firearms and ammunition.<INST> </INST></TTL><P>Any firearm, as well as discharged or intact ammunition, suspected of being involved in a criminal offense.</P></ITEM>
<ITEM><TTL><INST>8. </INST>Glass.<INST> </INST></TTL><P>Any glass particle or fragment that may have been transferred to a person or object involved in a crime. Windowpanes containing holes made by a bullet or other projectile are included in this category.</P></ITEM>
<ITEM><TTL><INST>9. </INST>Hair.<INST> </INST></TTL><P>Any animal or human hair present that could link a person with a crime.</P></ITEM>
<ITEM><TTL><INST>10. </INST>Impressions.<INST> </INST></TTL><P>Tire markings, shoe prints, depressions in soft soils, and all other forms of tracks. Glove and other fabric impressions, as well as bite marks in skin or foodstuffs, are also included.</P></ITEM>
<ITEM><TTL><INST>11. </INST>Organs and physiological fluids.<INST> </INST></TTL><P>Body organs and fluids are submitted for toxicology to detect possible existence of drugs and poisons. This category includes blood to be analyzed for the presence of alcohol and other drugs.</P></ITEM>
<ITEM><TTL><INST>12. </INST>Paint.<INST> </INST></TTL><P>Any paint, liquid or dried, that may have been transferred from the surface of one object to another during the commission of a crime. A common example is the transfer of paint from one vehicle to another during an automobile collision.</P></ITEM>
<ITEM><TTL><INST>13. </INST>Petroleum products.<INST> </INST></TTL><P>Any petroleum product removed from a suspect or recovered from a crime scene. The most common examples are gasoline residues removed from the scene of an arson, or grease and oil stains whose presence may suggest involvement in a crime.</P></ITEM>
<ITEM><TTL><INST>14. </INST>Plastic bags.<INST> </INST></TTL><P>A disposable polyethylene bag such as a garbage bag may be evidential in a homicide or drug case. Examinations are conducted to associate a bag with a similar bag in the possession of a suspect.</P></ITEM>
<ITEM><TTL><INST>15. </INST>Plastic, rubber, and other polymers.<INST> </INST></TTL><P>Remnants of these manufactured materials recovered at crime scenes may be linked to objects recovered in the possession of a suspect perpetrator.</P></ITEM>
<ITEM><TTL><INST>16. </INST>Powder residues.<INST> </INST></TTL><P>Any item suspected of containing firearm discharge residues.</P></ITEM>
<ITEM><TTL><INST>17. </INST>Serial numbers.<INST> </INST></TTL><P>This category includes all stolen property submitted to the laboratory for the restoration of erased identification numbers.</P></ITEM>
<ITEM><TTL><INST>18. </INST>Soil and minerals.<INST> </INST></TTL><P>All items containing soil or minerals that could link a person or object to a particular location. Common examples are soil imbedded in shoes and safe insulation found on garments.</P></ITEM>
<ITEM><TTL><INST>19. </INST>Tool marks.<INST> </INST></TTL><P>This category includes any object suspected of containing the impression of another object that served as a tool in a crime. For example, a screwdriver or crowbar could produce tool marks by being impressed into or scraped along a surface of a wall.</P></ITEM>
<ITEM><TTL><INST>20. </INST>Vehicle lights.<INST> </INST></TTL><P>Examination of vehicle headlights and taillights is normally conducted to determine whether a light was on or off at the time of impact.</P></ITEM>
<ITEM><TTL><INST>21. </INST>Wood and other vegetative matter.<INST> </INST></TTL><P>Any fragments of wood, sawdust, shavings, or vegetative matter discovered on clothing, shoes, or tools that could link a person or object to a crime location.</P></ITEM></NL>
<H1>The Significance of Physical Evidence</H1>
<P>The examination of physical evidence by a forensic scientist is usually undertaken for identification or comparison.</P>
<H2>Identification</H2>
<P><BOLD>Identification has as its purpose the determination of the physical or chemical identity of a substance with as near absolute certainty as existing analytical techniques will permit.</BOLD> For example, the crime laboratory is frequently asked to identify the chemical composition of an illicit-drug preparation that may contain heroin, cocaine, barbiturates, and so on. It may be asked to identify gasoline in residues recovered from the debris of a fire, or it may have to identify the nature of explosive residues—for example, dynamite or TNT. Also, the identification of blood, semen, hair, or wood would, as a matter of routine, include a determination for species origin. For example, did an evidential bloodstain originate from a human as opposed to a dog or cat? Each of these requests requires the analysis and ultimate identification of a specific physical or chemical substance to the exclusion of all other possible substances.<SIDEIND NUM="1" ID="MN2.03.001"/></P>
<P>The process of identification first requires the adoption of testing procedures that give characteristic results for specific standard materials. Once these test results have been established, they may be permanently recorded and used repeatedly to prove the identity of suspect materials. For example, to ascertain that a particular suspect powder is heroin, the test results on the powder must be identical to those that have been previously obtained from a known heroin sample. Second, identification requires that the number and type of tests needed to identify a substance be sufficient to exclude all other substances. This means that the examiner must devise a specific analytical scheme that will eliminate all but one substance from consideration. Hence, if the examiner concludes that a white powder contains heroin, the test results must have been comprehensive enough to have excluded all other drugs—or, for that matter, all other substances—from consideration.</P>
<P>Simple rules cannot be devised for defining what constitutes a thorough and foolproof analytical scheme. Each type of evidence obviously requires different tests, and each test has a different degree of specificity. Thus, one substance could conceivably be identified by one test, whereas another may require a combination of five or six different tests to arrive at an identification. In a science in which the practitioner has little or no control over the quality and quantity of the specimens received, a standard series of tests cannot encompass all possible problems and pitfalls. So the forensic scientist must determine at what point the analysis can be concluded and the criteria for positive identification satisfied; for this, he or she must rely on knowledge gained through education and experience. Ultimately, the conclusion will have to ...
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