Evidential Value of Trace Evidence - Essay Example

Discuss How the Evidential Value of Trace Evidence May Vary In An Investigation Depending on the Circumstances of an Incident and Evaluate the Impact of a Type of Trace Evidence in One Actual Case Trace evidence is a phrase used in the Crime Scene Investigation which refers to microscopic materials that are recovered from the scene of the crime and are used by the authorities as clues to the identity of the culprit as well as evidence in court to make a case against a suspect. The value of trace evidence in criminal cases was first brought to the fore by French scientist Edmund Locard when he formulated the Exchange Principle in early 1900s which states that “Whenever two objects come into contact, there is always a transfer of material (Snow 2005 p. 79). The principle also posits that the more violent the contact, the higher the possibility of the transfer and that a person’s body, including his clothing, is a rich source of trace materials that he accumulated from contact with things, persons and places. The main advantage of trace evidence is that their microscopic nature allows their transfer from one surface to another without detection by the naked eyes. However, trace evidence are not treated with equal weight when presented as evidence in courts but their value are considered on a case to case basis. Trace evidence include, among others, fingerprints, DNA, hair, lint from clothes, scratched paint, broken glass and dirt in shoes (Mozayani & Noziglia 2006 p 265). Trace evidence are processed in the laboratory by a trace evidence analyst, also known as a forensic scientist, and these microscopic evidence are characterized, identified and compared with other trace evidence in other cases, and introduced in court to comprise the evidence of a party (Houck 2003 p 1). Before they are processed however, they need to be collected carefully from the scene of the crime. It was Locard who recommended that trace evidence that can be seen by a magnifier should be collected using tweezers or needles and placed in folded paper packets. On the other hand, garments or clothing can be scraped, brushed or shaken for trace evidence over clean paper. When trace evidence are completely invisible to the naked eye, Dr. Max Frei-Sulzer of the Zurich Police Department Crime Laboratory recommended using transparent tape over the suspected area as a means of lifting the trace material. The same method of tape lift, albeit of a different type, can be used on gunshot residue (GSR) particles. GSR are examined under a scanning electron microscopy (SEM) which are collected from the hands or clothing of the suspect, particularly in areas where the gun made contact after it was fired (Mozayani & Noziglia 2006 p 266). The analysis of the trace evidence and their successful matching to suspects are not enough guaranties that the court will place great weight on them as evidence. The next step therefore is to determine the significance of the trace evidence to the incident and whether there is a great possibility that such evidence could have been present in the crime by chance and did not originate from the suspect although he was found positive of it. The worth of trace materials are dependent on their type, amount, location where they were found and the circumstances of the crime (Houck 2003 p 1). Human Hair. The rare features, as a result of natural characteristics or environmental factors, in human hair can give it valuable evidential value simply because there is less possibility that its presence in the crime scene is merely coincidental. Thus, hair that is long or chemically treated, or hair that has sustained damage have possible greater evidentiary value. A long strand of hair for example, can exhibit more features and characteristics than a short one, which can vary along its length. A chemically treated hair, on the other hand, by dyeing, bleaching, streaking and the like may exhibit both natural and chemical characteristics. Hair is estimated to grow at a rate of ½ inch a month and the untreated part of the hair may be used to calculate the time of the treatment. This information may be useful to investigate the activities of the suspect before the incident and find corroboration with third parties. Damaged hair is also valuable especially if violent crime is involved because it can signify violence and imply stronger association (Houck 2003 p 137). Barry Gaudette, a forensic scientist who made extensive studies on hair, formulated factors that tend to strengthen or weaken the evidential value of hair. The phrase “positive hair comparison was used by Gaudette to indicate that the sample hair and that of the suspect has many common characteristics and not to positively declare that hair is that of the suspect. The factors that strengthen the evidential value of hair are: “two or more mutually dissimilar hairs found to be similar to hairs in a known sample; hairs with unusual characteristics; hairs found in unexpected places; two-way transfer for example, a victim’s hair found on an accused clothing and accused hair found on the victim’s clothing, and; additional examination such as DNA testing” (Houck 2003 p 138). On the other hand, the following are factors that would tend to weaken the evidential value of hair, according to Gaudette: “the presence of incomplete hairs; questioned hairs that are common featureless hairs; hair of non-Caucasian racial origin; a questioned hair found in conjunction with other unassociated hairs, and; known samples with large intra-sample variation” (Houck 2003 p 138). Fiber. Fiber evidence can prove to be valuable in cases where a reconstruction of the events that occurred during and after the commission of the crime is vital. Fibers from a shooting victim, for example, could show up in a microscopic examination of bullets or fibers from someone who fired a shot or could be found in the gun used and discarded especially if had carried it inside his coat pocket. However not all fiber evidence have high evidential value all the time like in cases where the suspect is a relative or a close friend who frequents the victim’s home or area where the crime was committed because these trace evidence such as fibers could have been easily transferred at any time during one of his or her visits (Robertson & Grieve 1999 p109). An example where fiber evidence is very useful and could provide investigative leads is when the victim is abducted, killed, wrapped in a tarp and dumped in a ditch. If the killer owned Fig. 1 Ratio of Trace Evidence that can be found where victim is abducted, killed, wrapped and dumped (source: Robertson & Grieve, p110) the plastic tarp, it would contain most likely particles and trace evidence that come from his immediate environment such as hair, fibers, and others. Four kinds of materials are classifiable in this kind of incident: trace materials from the victim; trace materials from the killer; trace materials from the scene, and; the rest are miscellaneous. The most likely ratio is shown in Figure 1 (Robertson & Grieve 1999 p109). There are, however, types of fibers that forensic scientists find with least value because they are so common. An example of this is white cotton which is so common that their presence as trace materials in crime scenes is usually ignored by criminalists (Robertson & Grieve 1999 pp 109-110). Sample Case: Atlanta Child Murders Case The Atlanta Child Murders case is an example of how trace evidence had figured in a criminal case and successfully boosted the case of the prosecution against a suspect. In this case, thirty American-African children were found murdered and missing beginning in July 1979. At first, the authorities suspected multiple killers because of the different styles in killing. Eventually, however, a certain fiber served to link all these cases together making the authorities focused on a single suspect. Fibers characterized by yellowish-green color, together with some violet acetate fibers, coarse and lobed enough for the police to suspect it to be of carpet material were found in all the victims’ clothing. At first, the source of these fibers cannot be located. When the presence of the fibers were leaked to the press, naked bodies of the abducted children started appearing in rivers and police began to stake bridges and on one of these stake outs, caught the killer. Subsequently, a search order was issued allowing search of the killer’s home and vicinity. Among the evidentiary materials associating him to the killings were fibers of the same material found in the children’s clothing, along with others like the hair of the killer’s dog (Nickell & Fischer 1999 pp 75-81). Eventually, the manufacturer of the fiber was located and turned out to be the Wellman Corporation in Massachusetts which sold it as yarn to West Point Pepperell, a carpet maker company, which in turn used the yarn on its “English Olive” Luxaire carpet. These carpets were sold only in the Atlanta area in limited numbers. This particular fact rendered the associative value of the fibers found in the murdered children’s of strong evidentiary worth. In the course of the trial of the case, it was shown to the court that the odds of having similar carpets in the Atlanta area could be computed as 1 in 7,792. In addition there are 27 more types of fibers in 19 cases of the murdered children that were shared by those found in the victim and the killer’s environment, thereby strengthening and multiplying the fiber evidence. Not surprisingly, the jury found the killer guilty - a guilt that was supported and demonstrated best by the fiber evidence (Nickell & Fischer 1999 pp 75-81). References Blackledge, Robert, 2007. Forensic Analysis on the Cutting Edge: New Methods for Trace Evidence Analysis. Wiley-Interscience. Houck, Max M. 2003, Trace Evidence Analysis: More Cases in Mute Witnesses. Academic Press. Mozayani, Ashraf & Noziglia, Carla, 2006. The Forensic Laboratory Handbook: Procedures and Practice. Springer. Nickell, Joe & Fischer, 1998. Crime Science: Methods of Forensic Detection. University Press of Kentucky, 1998 Robertson, James & Grieve, Michael, 1999. Forensic Examination of Fibres. CRC Press. Snow, Robert L. 2005, Murder 101: Homicide and Its Investigation. Greenwood Publishing Group. Read More