Forensic Science
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Forensic Science

An Introduction to Scientific and Investigative Techniques, Fifth Edition

Suzanne Bell

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  1. 348 pages
  2. English
  3. ePUB (adapté aux mobiles)
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eBook - ePub

Forensic Science

An Introduction to Scientific and Investigative Techniques, Fifth Edition

Suzanne Bell

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À propos de ce livre

  • Showcases contributions from high-profile experts in the field

  • Highlights real-life case studies from experts' personal files, along with stunning full-color photographs

  • Organizes chapters into topics most popular for coursework

  • Covers of all forms of evidence, from bloodstain patterns to questioned documents

  • Includes textboxes with historical notes, myths in forensic science, and advice for career advancement

  • Provides chapter summaries, key terms, review questions, and further reading

  • Includes access to an identical eBook version

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CRC Press
Criminalistics (forensic science) is concerned with the unlikely and the unusual. Other sciences are concerned primarily with the likely and the usual. The derivation of equations, formulas, and generalizations summarizing the normal behavior of any system in the universe is a major goal of the established sciences. It is not normal to be murdered, and most persons never experience this unlikely event. Yet, when a murder occurs, some combination of circumstances suddenly alters the situation from unlikely to certain.
Paul Kirk
(1902–1970)American forensic scientist
One thing that all forensic disciplines share is an application of a tool, method, or technique to some aspect of the judicial system. Often this is law enforcement and criminal prosecution, but not exclusively. Biology becomes forensic biology with DNA typing, for example, and chemistry becomes forensic chemistry when chemical methods are used to analyze samples like plant ­matter or pills. The results of drug and DNA testing are used in legal matters, and so we describe these sciences as forensic science. Just as biology can be further categorized as cellular biology or microbiology, so too can forensic science be categorized into disciplines such as toxicology, death investigation, or trace evidence. In this book, we examine the most common forensic disciplines, but by no means all of them.
Myths of Forensic Science
Forensic scientists solve cases.
Forensic scientists are not crime scene heroes or courtroom magicians; they are scientists that analyze evidence to produce vital information. They are not tasked with solving crimes or catching criminals. Rather, the forensic scientist’s job is to contribute information that can be used to accomplish these goals. The data and information provided by forensic science is only part of a case—often a vital part, but it can never be the entire story.
The quote from Dr. Paul Kirk at the beginning of the chapter describes how forensic science deals with unique and rare events. The phrase “every case is different” has become a clichĂ© because it is true. No two murders, drug samples, firearms, and so forth, are the same, but how and why they are analyzed based on similar underlying concepts. Every crime scene is different, but physics can explain how blood moves and how it behaves when it strikes a surface. When you analyze many bloodstains at a crime scene and put the information together, the data can demonstrate what actions could have produced those stains or, just as importantly, what could not have happened. We will learn more about bloodstain patterns in Chapter 4, but all forensic analyses share this core characteristic of being useful in supporting or refuting possibilities or hypotheses regarding events that took place in the recent past.
Events that have occurred in the distant past are studied and evaluated using techniques of archaeology and the study of archaeological artifacts. As such, the discipline shares common elements with forensic science. Imagine that an archaeologist has found a promising site in a cave. Her hypothesis (a possible explanation or interpretation) is that early humans lived in this cave in the distant past (Figure 1.1). The next task is to gather data and information from the site to evaluate this idea. Next would come a lengthy excavation of the site during which artifacts and evidence would be recovered. If none were recovered, the scientist would have to revise her hypothesis or abandon it, but she would do so based on data and information. In this example, assume she did recover artifacts that included small animal bones with striation marks, sharp rocks, charcoal, and a few human bones piled together neatly at the far back of the cave. These items are physical evidence. Taken alone, this evidence does not tell us what happened in the cave tens of thousands of years ago, but it does support the hypothesis that people once inhabited the cave.
FIGURE 1.1 An archaeological excavation. Image courtesy of the National Parks Service.
There is still much work to be done with the evidence. For example, the archaeologist could send the bone fragments to an expert to see if the striation marks on the animal bones were made by some form of primitive knife or axe. Another expert could look at the sharp rock and determine if it was artificially shaped by chipping to make it into a tool. Specialized laboratories could be used to estimate the date when the wood was burned. All this information becomes data that the archaeologist would use to evaluate her hypothesis.
Suppose the rock was determined to be a tool, the marks on the animal bones were from a primitive knife, and the charcoal dated back tens of thousands of years. Add this data to finding human bones in the cave, and all the evidence supports the archaeologist’s original hypothesis—humans did occupy this site in the distant past. On the other hand, imagine that the marks on the animal bones were found to be nothing more than damage accumulating over the years and the sharp rock was just that and not a tool. Knowing that, the archaeologist must reconsider her ideas. Perhaps the evidence is there and has yet to be found, or maybe it was there but long since washed away. New data means that interpretations must be reexamined. The data always shapes conclusions—that is the essence of the science of forensic science.
1.2 Forensic Science and Competing Stories
Data generated by forensic scientists are often used to support or refute different versions of recent events rather than events from the distant past. In the legal context, this could be a suspect’s version of an event compared with an investigator’s or prosecutor’s version of that same event. Suppose police are called to the scene of a fatal shooting. They find a relative of the victim and his clothes are heavily stained with what appears to be blood. This person is identified as the victim’s brother. Police call the crime scene unit to process the scene, collect evidence, and deliver it to laboratory. The information provided will be integrated into the investigation and used to determine what could have happened and, just as importantly, what could not have happened.
The suspect (the victim’s brother) might claim that he was upstairs, heard a shot, and ran down to find his brother mortally wounded. He called 911 and comforted him until help arrived. This is the suspect’s story. On the other hand, investigators might initially believe that the suspect purposely shot and killed his brother after a heated argument and the blood on his clothes shows that he was standing close to the victim when the shot was fired. Both stories are initially plausible, and the investigation will begin. The role of the crime scene investigator would be to document and collect evidence at the scene and deliver it to the appropriate forensic scientists for examination. In turn, the scientists will examine the evidence and generate reports that will become part of the body of evidence in the investigation. Table 1.1 illustrates the type of information and findings that could be produced in the example shooting case.
TABLE 1.1 Example Findings
Determined by
Story Supported
The brother called 911
Cell phone records
The stains on the suspect’s clothing were blood
Forensic laboratory analysis
DNA results showed the blood to be that of the victim
Forensic laboratory analysis
A gun was found at the scene
Crime scene investigator
One set of fingerprints on...

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