The Weight of Evidence and the Burden of Proof

One of the constants of forensic science is how frequently its applications become front-page news. Whether the story is sniper shootings or the tragic consequences of the terrorist attacks of 9/11/01, forensic science is at the forefront of the public’s eye. In this new century, the science of DNA profiling has altered the complexion of criminal investigation. DNA collected from saliva on a cup or from dandruff or sweat on a hat exemplifies the emergence of nontraditional forms of evidence collection at crime scenes. Currently the criminal justice system is creating vast data banks designed to snare the criminal who is unaware of the consequence of leaving the minutest quantity of physical evidence behind at a crime scene. Like all facets of modern life, forensic science has undergone dramatic advances as technology and instrumentation has improved. This course will introduce the student to the basic concepts of science that are the foundation on which forensic science is based and then show how that knowledge is made relevant to criminal investigations. The nature of physical evidence is defined, and the limitations that technology and current knowledge impose on its identification and characterization are examined. As a result of this, myths perpetrated by popular CSI-like-television shows will be debunked. Forensic science begins at the crime scene. The principles and techniques of forensic science plus statistical and probabilistic reasoning shape the preparation of cases for prosecution. However, even when evidence is scientifically valid, it may not be used in a subsequent criminal case. The US criminal justice system introduces new factors, considerations, and biases. Prosecutors, defense attorneys, judges, and juries shape how and whether evidence is presented and how it is interpreted. This course will also present cases of prosecutorial abuse when the results of scientific testing of evidence are misrepresented as being conclusive to a jury when, in fact, it is not. The efforts of members of the Innocence project will be presented. Students will learn what each step along the evidentiary journey involves and how people and procedures can turn evidence into something irrelevant or the critical determinant of guilt and innocence. Likewise, there is a dire need to bridge the “communication gaps” that currently exists among lawyers, judges, juries and the forensic scientist. An intelligent evaluation of the scientist’s data and subsequent testimony requires some familiarity among legal professionals with the underlying principles of forensic science. It is hoped that this course will provide a painless route to comprehending the nature of the science and the criminal just system.