Forensic identification expertise encompasses fingerprint, handwriting, and firearms (“ballistics”), and toolmark comparisons, all of which are used by crime laboratories to associate or dissociate a suspect with a crime. Shoe and tire prints also fall within this large pattern evidence domain. These examinations consist of comparing a known exemplar with evidence collected at a crime scene or from a suspect. Bite mark analysis can be added to this category, although it developed within the field of forensic dentistry as an adjunct of dental identification and is not conducted by crime laboratories. In a broad sense, the category includes trace evidence such as the analysis of hairs, fibers, soil, glass, and wood. Some forensic disciplines attempt to individuate and thus attribute physical evidence to a particular source—a person, object, or location.1 Other techniques are useful because they narrow possible sources to a discrete category based upon what are known as “class characteristics” (as opposed to “individual characteristics”). Moreover, some techniques are valuable because they eliminate possible sources.
Following this introduction, Part II of this guide sketches a brief history of the development of forensic expertise and crime laboratories. Part III discusses the impact of the advent of DNA analysis and the Supreme Court’s 1993 Daubert decision,2 developments that prompted a reappraisal of the trustworthiness of testimony by forensic identification experts. Part IV focuses on the 2009 National Research Council (NRC) report on forensic science.3 Parts V through X examine specific identification techniques: (1) fingerprint analysis, (2) questioned document examination, (3) firearms and toolmark identification, (4) bite mark comparison, and (5) microscopic hair analysis. Part XI considers recurrent problems, including the clarity of expert testimony, limitations on its scope, and restrictions on closing arguments. Part XII addresses procedural issues—pretrial discovery and access to defense experts.
1. Some forensic scientists believe the word individualization is more accurate than identification. Paul L. Kirk, The Ontogeny of Criminalistics, 54 J. Crim. L., Criminology & Police Sci. 235, 236 (1963). The identification of a substance as heroin, for example, does not individuate, whereas a fingerprint identification does.
2. Daubert v. Merrell Dow Pharms., Inc., 509 U.S. 579 (1993). Daubert is discussed in Margaret A. Berger, The Admissibility of Expert Testimony, in this manual.
3. National Research Council, Strengthening Forensic Science in the United States: A Path Forward (2009) [hereinafter NRC Forensic Science Report], available at http://www.nap.edu/catalog.php?record_id=12589.