RELATIONSHIPS AND CONTEXT
The relationships between the people, places, and things involved in crimes are critical to deciding what to examine and how to interpret the results. For example, if a sexual assault occurs and the perpetrator and victim are strangers, more evidence may be relevant than if they live together or are sexual partners. Strangers are not expected to have ever met previously and, therefore, would not have transferred evidence before the crime. People who live together would have some opportunities to transfer certain types of evidence (head hairs and carpet fibers from the living room, for example) but not others (semen or vaginal secretions). Spouses or sexual partners, being the most intimate relationship of the three examples, would share a good deal of more information. The interaction of these evidence environments is shown in Figure 3.4. Stranger-on-stranger crimes beg the question of coincidental associations; that is, two things which previously have never been in contact with each other have items on them which are analytically indistinguishable at a certain class level. Attorneys in cross-examination may ask, “Yes, but couldn’t [insert evidence type here] really have come from anywhere? Aren’t [generic class-level evidence] very common?” It has been proven for a wide variety of evidence that coincidental matches are extremely rare. The variety of mass-produced goods, consumer choices, economic factors, and other product traits creates a nearly infinite combination of comparable characteristics for the items involved in any one situation. Some kinds of evidence, however, are either quite common, such as white cotton fibers, or have few distinguishing characteristics, such as indigo-dyed cotton from denim fabric. “Common,” however, is a word to be used with caution and even then only after a thorough knowledge of how that material is produced, either naturally or artificially and how it varies. Even materials that are thought to be “common” can have a high variance (see Figure 3.5). It is important to establish the context of the crime and those involved early in the investigation. This sets the stage for what evidence is significant, what methods may be most effective for collection or analysis, and what may be safely ignored. Using context for direction prevents the indiscriminate collection of items that clog the workflow of the forensic science laboratory. Every item collected must be transferred to the laboratory and catalogued—at a minimum—and this takes people and time. Evidence collection based on intelligent decision-making, instead of fear of missing something, produces a better result in the laboratory and the courts.
FIGURE 3.4 The significance of the interaction between the victim(s) and the criminal(s) at one or more crime scenes is largely determined by the relationships between the people, places, and things involved. Strangers have a different relationship than do spouses or family members. People who live together have more opportunities to transfer evidence on a regular basis than do strangers. Spouses or sexual partners, being more intimate, would share more information.
FIGURE 3.5 Forensic scientists need to learn the details about the materials they study and analyze as evidence—even something perceived to be very common, like sand, can have a wide variation. Top to bottom: Rodeo Beach, Marin County, CA; Agate Beach, OR; Daytona Beach, FL; Bermuda; Sanorini, Greece; Ayers Rock (Uluru), Australia; Sahara Desert, Mauritania; Old Course Beach, St. Andrews, Scotland.
