A common theme in all criminal investigations, and one of the most important throughout this text, is the collection of physical evidence. While the topic of physical evidence is addressed in several chapters of this book, the chapter specifically focuses on the techniques used to identify, collect, package, and store particular types of physical evidence for subsequent examination.
Several types of physical evidence are covered in this chapter: soil and pollen, footwear and tire prints, paint, glass, fibers, hair, lip prints, and tool marks. Details on collection and packaging techniques are provided for fingerprints, dental evidence, bloodstains, firearm evidence, and questioned documents. In addition, several software programs and investigative tools for each type of evidence is discussed. The importance of consulting specialized forensic and medical experts is emphasized throughout the chapter.
Due to inattention, neglect, or simply oversight, there may be occasions when investigators fail to collect potentially important physical evidence at a crime scene. As a rule of thumb, investigators should immediately collect any and all types of physical evidence. Even if the source of crime scene samples is unknown at the time, investigators may later be able to connect the samples to a source in the same, or perhaps in another, criminal investigation. In short, once a crime scene is released, the chance of collecting any evidence that has not either been destroyed or been contaminated from a variety of factors is essentially nonexistent. Lack of evidence significantly hampers investigators’ ability to produce a strong criminal case against a defendant; in addition, most investigators agree that there is nothing worse than being questioned at a trail about their lack of or careless collection of evidence.