KNOWN AND QUESTIONED ITEMS
Continuing with the hit-and-run example, say a motorist strikes a pedestrian with his or her car and then flees the scene in the vehicle. When the pedestrian’s clothing is examined, small flakes and smears of paint are found embedded in the fabric. When the automobile is impounded and examined, fibers are found embedded in an area that clearly has been damaged recently. How can this evidence be classified? The paint on the victim’s coat is questioned evidence because we don’t know the original source of the paint. Likewise, the fibers found on the damaged area of the car are also questioned items. The co-location of the ibers and damaged area and the wounds/damage and paint smears are indicative of recent contact. When we analyze the paint on the clothing, we will compare it to paint from the car; this is known evidence because it is known where the sample originated. When we analyze the fibers on the car, we will compare them to fibers taken from the clothing, which makes them known items as well. Thus, the coat and the car are sources of both kinds of items, which allow for their re-association, but it is their context that makes them questioned or known. Back at the scene where the body is found, there are some pieces of yellow, hard, irregularly shaped material. In the laboratory, the forensic scientist will examine this debris and will determine that it is plastic, rather than glass and further it is poly propylene. This material has now been put in the class of substances that are yellow and made of polypropylene plastic. Further testing may reveal the density, refractive index, hardness, and exact chemical composition of the plastic. This process puts the material into successively smaller classes. It is not just yellow polypropylene plastic but has a certain shape, refractive index, density, hardness, etc. In many cases, this may be all that is possible with such evidence. We have not been able to determine the exact source of the evidence, but only that it could have come from any of a number of places where this material is used—class evidence. Suppose that the car suspected to be involved in the hit-and-run case has a turn signal lens that is broken and some of the plastic is missing. The pieces are too small and the edges too indefinite for a physical match. Pieces of this plastic can be tested to determine if it has the same physical and chemical characteristics as the plastic found at the crime scene (color, chemical composition, refractive index, etc.). If so, it could be reported that the plastic found at the scene could have come from that broken lens. This is still class evidence because there is nothing unique about these properties that would be different from similar plastic turn signal lenses on many other cars.
