DEVELOPING FORENSIC INVESTIGATIVE LEADS THROUGH THE MICROSCOPICAL EXAMINATION OF TRACE EVIDENCE

A fundamental consequence of scientific logic (and geological knowledge) is that scientific theories can be disproved, but never proved. Forensic science, can at times however, provide a unique exception to this rule because the ultimate answer is known, though it may be only by the criminal whom the laboratory and investigators are attempting to implicate.

In numerous cases in which our laboratory has provided direction or forensic evidence to investigators, subsequent arrests, confessions, and convictions have elicited information from a criminal that has provided direct confirmation of the scientific hypotheses (known in a forensic context as “investigative leads” or “expert opinions”) developed during our investigation. These investigative leads are hypotheses that have been developed directly from factual information extracted from the scientific examination of physical evidence recovered in the course of a criminal investigation. This forensic evidence is often present only in microscopic quantities and can consist of any conceivable material.

This presentation will discuss the evidentiary value of these types of microscopic materials with an emphasis on geologic and geologically derived trace evidence and the ways in which this evidence can be located, isolated and examined to establish factual evidence. A combination of these facts derived from any materials present (e.g., minerals, pollen, paint, fibers) can be exploited to place constraints on the occupation or habits of a suspect being sought. These materials can also provide information about an unknown environment of interest at a variety of length-scales. For example, geological evidence from a single sample might be used to provide a broad regional description of an unknown area or, it may be used to associate evidence with a specific address on the basis of some more unusual trait (e.g., unexpected pollen or an unusual suite of minerals). In some cases, a single sample can provide both types of information. In any scenario, however, the importance of a complete analysis of all available evidence, which will always spans multiple disciplines, will be illustrated through case examples from our laboratory in which theories developed to provide investigative aid have been confirmed as fact through the admission or capture of criminals themselves.