THE BASIS OF EVIDENCE: INDIVIDUALIZATION OF EVIDENCE
A definition for individualization was offered in the preceding section, that is, categorizing an item in a set or class that has one and only one member. To that extent, individualization is the logical extension of classification. The concept of individualization rests on two assumptions:
• All things are unique in space and time; and
• The properties by which a thing is classiied are constant over time.
Without these assumptions being in effect, statements such as “Yes, that is a Phillips head screwdriver and it is mine,” could not be properly understood. Ques tions (“What’s a screwdriver? What’s a ‘Phillips head’ mean? How do you know it’s yours?”) would plague even the simplest statements. These two assumptions come with baggage, however. First, the assumption of uniqueness of space is an inherently non-provable situ ation. The population size of “all things that might be evidence” is simply too large to account for; think of all the fingerprints on all the surfaces all over the world.
A contributing factor to this is, throughout its history, forensic science has been case work driven, not research driven. Thus, many principles and concepts are derived from years of work-related experience, which is, regrettably, inconclusive from a research standpoint. A jury may reach a decision, a person may confess, and an accomplice may inform, but from a purely scientific perspective, we do not know what really happened. In a laboratory experiment, the scientist has control of all the variables of interest except one; any change in those variable leads to a stronger cause and-effect statement. In forensic science, the scientist has absolutely no control over the circumstances during the crime. Put a bit more simply, casework is not research. Second, things do not stay the same over time or change at the same rate. The value of some forensic evidence, in fact, is based on it changing over time, like shoe prints. Not knowing the amount and rate of change can hamper the interpretation of evidence and its interpretation. Forensic science is relegated to making interpretive statements based on statistical methods because it deals with so many uncertainties. As Schum clearly explains, Schum’s point is that if scientists were absolutely certain of their samples or the accuracy of their methods, statistics would not be needed. Forensic science deals with the ultimate uncertainties in the real world of criminal activities with varying physical objects. The gap between the controlled laboratory and the real world is central to forensic science’s fundamentals: Uncertainty is everywhere. Even in DNA analysis, where each person’s genetic material—except for identical twins—is known to be unique, statistics are used. Statistics are, in fact, what give forensic DNA analysis its power. Does this mean, then, that individualization is a bankrupt concept? Only if it is considered as a provable scientific statement. Consider two statements:
1. A forensic scientist says, “The questioned item came from the known source to the exclusion of any other similar object that currently exists, has ever existed or will ever exist.”
2. A friend says, “This is my friend Howard.” Both are statements of individualization. Statement #2 is provable in a personal sense; that person knows Howard to the exclusion of anyone else he or she might meet. Statement #1, however, is problematic in that one could not possibly check all other similar items currently in the world, let alone all that have ever existed or ever will exist (this is not an extreme statement taken out of context, some forensic examiners still testify this way) to absolutely ascertain that the questioned item came from the known source and only the known source.
Forensic scientists are beginning to recognize the complexity of their evidence and are adjusting their methods. Recent work on fracture matches, where an item has been physically broken into two or more pieces and those pieces are positively associated, promises hope for a statistical treatment of forensic interpretations. The innumerable variables, such as force used to break the object, shape of the object, microstructure and chemical nature of the material, and direction of the blow, all lead to those characteristics that forensic scientists use to compare the fragments. These can lead to exciting research and applications of physics, chemistry, materials science, and nanoscience.
