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Forensic Science and Technology By Robert E. Gaensslen, Professor, Director of Graduate Studies, Head of the Program in Forensic Science, University of Illinois at Chicago Dr. Gaensslen (Ph.D., Cornell, 1971) is an expert in biological evidence examination, DNA forensic technology, and forensic laboratory approaches in the criminal justice system. He has coauthored seven books, coauthored nine chapters in edited volumes, and published over 60 papers in the refereed scientific literature. He has also organized, coordinated, and participat- ed in dozens of workshops and training courses for forensic science laboratory and law enforce- ment personnel. Dr. Gaensslen is a fellow of the Criminalistics Section, American Academy of Forensic Sciences. He has received the Paul L. Kirk Distinguished Criminalist Award from the Criminalistics Section and was made a distinguished fellow by the Academy in 2000. He is a life member of the Northeastern Association of Forensic Scientists. I assure you that we are returning to the macro level for the next half hour. Within the field of forensic science, criminalistics can be organized according to the kinds of evidence examined in a crime lab. Using this scheme, let me sort the field into chem- ical, biological, trace, and pattern evidence. Instrumental analysis is deeply interwoven with the analysis of chemical, trace, and bio- logical evidence. Forensic investigators who are analyzing materials from a crime scene typically have three goals: classification, individualization, and reconstruction. They are particularly interested in establishing the uniqueness of a piece of evidence. People in quality control think about how to make things the same, but I don't know anyone else who works on materials who thinks about how to render things unique! With chemical evidence, the basic task is to identify a material. What is this, and how much is there? Chemical analysis can be further broken down into two categories: elemental analysis and organic compound analysis. Both are particularly dependent on instruments. A good example is identi- fying gunshot residue. Gunshot residue can consist of smoke, debris, foreign parti- cles, or other substances. These materials are emitted by a gun and are deposited on the hand of the shooter or on anyone or anything else in the vicinity. Law enforce- INSTRUMENTATION FOR A BETTER TOMORROW 43
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ment personnel are very interested in the analysis of gunshot residue in the hope that the results of such an analysis will show that someone fired a weapon. Unfortunately, even if the identification of gunshot residue is rigorous, it does not prove that the hand fired the weapon--only that the hand was in the vicinity. In the 1970s many forensic labs became interested in a The identification technique known as neutron activation analysis to iden- tify materials. But it proved less useful than anticipated. of organic The cost and difficulty of the technique were part of the problem, and it promised more than it could deliver. There were so many variables associated with the ele- compounds mental profiles of materials that it proved very difficult Beckman Instruments executives examine mass spec- to establish uniqueness. This is an example of a tech- trometer in 1953. Courtesy Beckman Coulter, Inc. has been nique that comes along that is instrument-based and chases applications. revolutionized Today gunshot residue is usually analyzed using a combination of scanning electron by instrumental microscopy to visualize the particles and a technique known as energy dispersive x-ray analysis to analyze elemental constituents. It is the combination that lets you make the identification. But the problem of linking the residue to the shooter remains. The presence methods. of gunshot residue on a hand does not make that person the shooter, and that's the ques- tion the police are interested in answering. The identification of organic compounds has been revolution- ized by instrumental methods. The methods used most often include gas chromatography and liquid chromatography with mass spectrometry. Much of this work involves identifying illicit drugs. For example, the Chicago lab of the Illinois State Police Varian CP-3800 Gas chromatograph. Courtesy of Varian, Inc. 44 INSTRUMENTATION FOR A BETTER TOMORROW
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handles about 5,000 cases per month, of which more than 4,000 are drug cases. And agents will tell you that they are getting only 1 or 2 percent of the drug traffic. The illicit drug problem continues to dominate the lab landscape. The workhorse instrument in the lab for the analysis of trace materials has always been the microscope, which provides a rapid, convenient, and nondestructive method for viewing such materials as hairs, fibers, and paint. A microscope can be used to identify and some- times partly to individualize these materials, but caution is warranted. For example, many forensic examiners recognize that hair samples cannot be individualized, but some of them We are nevertheless have testified with a greater degree of confidence than was warranted. When DNA evidence became available, these mistaken identifications became apparent. Quite a natural few reputations of labs and examiners, whether they acted out of ignorance or because of misguided efforts to please prosecutors, have been destroyed in the process. beneficiaries Today, analysis of biological evidence consists mostly of DNA profiling. However, an essential of the element of this profiling is the sampling and identification steps that precede the actual analy- legacy of sis of DNA. An important consequence of DNA profiling has been the enablement of construct- Dr. Beckman. ing databases of offenders. Every state in the nation has passed legislation mandating the databasing of DNA profiles of criminals. Some databases include only those convicted of sexual assaults, while others include all felony offenders, and the trend is in the direction of databasing more people, not fewer. Despite relatively efficient typing or profiling methods, databasing and casework demands have overwhelmed many forensics laboratories. Part of the reason is that the front-end processing of material is still very labor intensive. It requires judgment and is difficult to automate. The federal government and the states are working to alleviate this problem. Meanwhile, there are many opportunities for automation and innovation to address databasing bottlenecks. INSTRUMENTATION FOR A BETTER TOMORROW 45
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A critical issue for forensic laboratories is the admis- sibility of forensic evidence in court. The 1992 Supreme Court case Daubert v. Merrell Dow Pharmaceuticals addressed this concern. The case established that scientific evidence presented in a court has to have a solid scientific underpinning, and it established guidelines for making this deter- mination. Establishing the scientific underpinnings for a particular argument can be particularly diffi- cult for pattern evidence. Even in the case of finger- prints, which are widely accepted as being unique, the scientific validity of that uniqueness has never been demonstrated. Biometric specialists are now addressing this issue, but considerable work still needs to be done to establish standards and tech- niques for the use of fingerprint evidence (Figure 22). Another example involves identifying bullets from particular firearms. Each handgun or rifle makes distinctive marks on the casing of a bullet, and these marks can be observed and assessed to determine if a bullet was fired from a particular gun. Recently, I have been participating in experiments on consecu- tively manufactured gun barrels to determine the extent to which any two firearms can be distin- guished. The marks are different, but not by much. FIGURE 22 The sophistication of modern law enforcement has greatly increased with the advent of new technologies. Forensic science is by definition an applied enter- Computer databases of fingerprints, chemical testing, and genetic analysis are among the many advanced tools used prise, using scientific, technological, and analytical in such investigations. methods to answer questions that are involved in legal and regulatory matters. We are natural benefi- ciaries of the legacy of Dr. Beckman. 46 INSTRUMENTATION FOR A BETTER TOMORROW