Figure 1
The eight steps.
Abstract: The increasing number of recent courtroom challenges to various areas of forensic science has forced examiners to re-examine their methods of explaining analyses. Although the methodology involved in these disciplines is generally sound, many examiners have difficulty putting into words the steps involved in reaching their conclusions. This article addresses the discipline of bloodstain pattern analysis and attempts to describe an easy-to-understand methodology that can be articulated in the courtroom.
To the layman, experts appear to act on instinct. This is true when listening to a classical pianist perform a complicated piano concerto, and this is no less true when listening to an experienced crime scene reconstructionist recite his or her conclusions regarding a complicated bloodstain pattern analysis without a supporting explanation. Although the layman understands that education, training, experience, and practice are all necessary to reach any degree of expertise, it is still difficult for him to comprehend exactly how all that background ends up synthesized into the final result. This difficulty is also shared by jurors, judges, and attorneys, and unfortunately, can result in questioning the scientific validity of some forensic disciplines. Furthermore, this problem of not fully understanding the steps that will ultimately lead to a valid scientific conclusion does not lie solely with those outside the forensic community. Many qualified experts in bloodstain pattern analysis will be able to come to complicated conclusions quite accurately, but may have trouble explaining just how they arrived at their results. These experts are most likely following a scientific methodology; however, they may never have stopped to think exactly what that methodology is.
The recent attacks on the validity of latent print identification have prodded the latent print community to examine in detail just exactly how and why identifications are made. As a result, the discipline of friction ridge identification has grown stronger and its examiners more confident in their conclusions. This article attempts to lay out a discrete bloodstain pattern analysis methodology that can be articulated to judges and attorneys to dispel any questions about the lack of scientific validity in the discipline.
One way to show that a forensic discipline is based upon sound scientific principles is to show that it conforms to the scientific method. It would seem simple enough, then, to write down the steps in the scientific method and then show a correspondence between these steps and the steps involved in the discipline in question. However, if one begins researching to find out just what those steps are, one discovers rather quickly that there is no single accepted version of the scientific method. Depending upon the source, the scientific method consists of as few as four steps or as many as eleven. Furthermore, there are dissimilarities both in the names of the steps and in the sequence in which they are to be carried out.
It is important to note, then, that a single scientific method does not exist, at least not as a standard list of steps that are common to all areas of science. And therein lies a major problem regarding the legal view of various forensic disciplines, to include that of bloodstain pattern analysis. Henry H. Bauer tells us, “So long as science is viewed as monolithic, founded on the scientific method, it is possible (and therefore irresistibly tempting) to label some sciences, or some bits of science, as ‘more scientific’ than others, according to the degree to which the method has been or can be successfully deployed.”[1] Indeed, bloodstain pattern analysis has been attacked in court as being one of those “lesser” sciences or, worse yet, as a so-called pseudoscience [2, 3].
Despite the nonexistence of a universal scientific method, it remains important to explain bloodstain pattern analysis and crime scene reconstruction in accordance with traditional views of science. In furtherance of this goal, Bevel and Gardner have devised a template for the scientific method that can be used in bloodstain pattern analysis [4]. This template is quite useful for the purpose of reminding the analyst that the analysis should follow a logical progression of evidence observation and the testing of hypotheses, but even the authors agree that this does not mean that the analyst should be tied down to a specific series and sequence of analytical steps. Gardner states quite correctly that the product of the scientific method is “an everexpanding, self-correcting body of knowledge”[5]. And Bevel and Gardner give a rather succinct, yet general definition of the scientific method as “a defined process used to resolve complex problems”[6].
And so, in order to substantiate this ever-expanding, selfcorrecting body of knowledge arrived at through the careful and painstaking analysis of bloodstain patterns, it is becoming necessary for each analyst to define his or her process to the satisfaction of those involved in criminal proceedings. And although it is true that most analysts’ individual methods may vary without any danger of compromising the validity of their conclusions, there are a number of basic and accepted scientific principles that can be identified when examining the process of bloodstain pattern analysis.
Dividing the methodology into separate steps will make it easier to understand what is going on in each phase of the analysis (Figure 1). It is important to remember, however, that although these steps are generally followed in a chronological order, there will often be occasion to backtrack and to repeat certain steps. Indeed, this is perfectly acceptable in any scientific methodology and can be observed in the ACE-V method used by latent print examiners.
The bloodstain analyst needs something to analyze; therefore, the first step in the process is to gather data. Data, in this case, can be defined as any information that can assist the analyst in determining what may or may not have happened before, during, or after the incident. Data may come from, but is not limited to, the following sources:
These might include photos of the crime scene, the victim (to include hospital and autopsy photos), any physical evidence (clothing or other bloodstained items), suspects and witnesses (especially if bloodstains are visible), vehicles (to show the presence or absence of bloodstains), and so forth.
These are crime scene reports, laboratory reports, autopsy reports, reports of suspect and witness interviews, and so forth.
Rough sketches and finished diagrams of the crime scene can help put the scene into perspective for the analyst.
Any physical evidence that the examiner feels could be pertinent to the analysis should be examined firsthand, even if there are photographs in which the evidence appears. Bloodstains on physical evidence, such as clothing, bedding, weapons, and so forth, may not be sufficiently visible in photographs.
There are many instances in which the bloodstain pattern analyst was never present at the crime scene or even involved in the initial investigation. In this situation, the analyst should spend some time becoming familiar with the case at hand. The data gathered during Step 1 can be used for this purpose. Here, the analyst is not interpreting the data; rather, he is making an attempt to learn as much about the case as possible. Reviewing crime scene reports, photographs, and diagrams can help the analyst get a feel for the scene. If at all possible, the analyst should consider visiting the crime scene as well.
Even if the analyst was involved with the investigation to begin with, and even if the analyst processed the crime scene himself, it is still helpful to take the time to refamiliarize oneself with the case. This is especially true if a long period of time has elapsed between the initial scene and the beginning of the bloodstain analysis.
Once the analyst is familiar with the case, individual bloodstain patterns that were observed at the scene, in photographs, on physical evidence, and so forth should be described. The location and appearance of cast-off patterns, drip patterns, f low patterns, impact patterns, and the like should be listed and then analyzed in a descriptive, yet nonsubjective, manner. For example:
Elliptical stains on kitchen f loor measuring approximately 1 - 4 mm in diameter. Stains have a linear configuration with southwest to northeast directionality and are consistent with a cast-off pattern.
In this step, the stains or stain patterns are being isolated and analyzed objectively and there is no attempt to infer the meaning of these stains or to associate the stains with the positions and movements of people at the crime scene. Note that this observation and analysis of the stains and stain patterns takes place before the patterns are compared with statements and theories put forth by suspects, witnesses, officers, and attorneys. This will help to demonstrate that the analysis (or at least this part of the analysis) is done in a completely objective manner, a point that is often challenged in court proceedings.
The hypotheses in this step will originate from various sources. Statements made during the interviews of suspects and witnesses are a source of hypotheses. Ideas suggested by investigators and attorneys can also be viewed as hypotheses. And, of course, the bloodstain analyst will also come up with hypotheses that need to be tested. It is important at this point that each hypothesis be limited to a single event or, at the very least, related events in order to avoid confusion. The analyst is not attempting here to devise a theory to explain everything that took place at the scene.
Here is an example of a statement made by a suspect during an interview, from which we can derive a usable hypothesis.
Mr. Andrews states that after Mr. Smith is on the bed and in a defensive posture with his arms and his legs up, Mr. Jones goes to the bed and repeatedly stabs Mr. Smith.
Once the hypothesis is stated, it needs to be tested. Testing of hypotheses can be carried out by employing certain scientific processes: empirical observation (to include the measurement of stains and stain patterns and the calculations derived therefrom, much of which will have been completed during Step 3); experimentation (the recreation of stain patterns); and logical reasoning (both deductive and inductive). Following the empirical observation or experimentation, logical reasoning will provide the answer as to whether or not the hypothesis is valid.
Now let us look at the earlier suspect statement (hypothesis), followed by the analysis (test).
Hypothesis: After Mr. Smith is on the bed and in a defensive posture with his arms and his legs up, Mr. Jones goes to the bed and repeatedly stabs Mr. Smith.
Test: Transfer and drip patterns on the bed covers are consistent with a struggle taking place on the bed after the victim has been stabbed. Cast-off stains on the ceiling above the bed, the area of the west wall between the bed and the nightstand, the northwest corner of the bed sheet, and on the south end of the nightstand are consistent with blood being thrown off an object (possibly a bloodstained knife). Wounds on Mr. Smith’s arms are consistent with being in a defensive posture during the stabbing and with the transference of additional blood on the bed covers.
In the above example, the hypothesis derived from the statement made by one of the suspects is consistent with the physical evidence as observed and analyzed by the bloodstain analyst. This opinion is arrived at only after the pertinent bloodstains are examined (empirical observation) and the results of this examination are compared with the statement of the suspect (logical reasoning).
The theories in this step are the possible scenarios that would account for the bloodstains and other physical evidence present at the scene. Theories are much broader than hypotheses and could include, among other things, the positioning of victims, suspects, or witnesses during or following bloodshed; various events or actions that took place and the possible sequence of these events; and the specific actors involved in the events. In a sense, a theory is a culmination of the validated hypotheses. And as in the case of the hypotheses, as each theory or scenario is formulated, it should be tested, in its entirety, against the evidence. The testing of theories is performed primarily through inductive and deductive reasoning.
When testing theories, it is important that the analyst not simply ignore those bits of physical evidence that do not immediately conform to the theory being tested. In some cases, additional analysis may reveal how this extraneous evidence fits in; however, the analyst must always be conscious of not forcing the evidence to fit the theory. In some cases, the extraneous evidence may contradict the theory, rendering the theory invalid. A new theory must then be devised and tested. In still other cases, the extraneous evidence may not invalidate the theory, but may instead suggest additional events, the occurrence of which were not initially considered.
The analyst’s conclusions should be supported by the physical evidence. When writing conclusions, it is always better to say too little than to say too much. Regardless of the opinion of the side by which the analyst has been hired, a competent bloodstain pattern analyst, when reporting a conclusion, will remain true to the observable evidence.
Very often, because of limited evidence that is available to the analyst, a bloodstain pattern analysis will suggest multiple plausible theories or scenarios. As such, the analysis may not be particularly helpful to either side in a criminal proceeding. In many other cases, however, the analysis may provide the definite elimination or exclusion of a particular scenario. This is often quite valuable information, because it may invalidate either the prosecution’s or the defense’s case. The aim of the analyst’s conclusions should be to provide the most likely scenario (or scenarios) based upon the objective examination of the evidence, followed by clear deductive and inductive reasoning. It is rare, if ever, that the bloodstain analyst will be able to come to a single definitive scenario that explains everything that took place at the scene.
In light of the rising number of legal challenges to various areas of forensic science, it is becoming significantly more important to be able to articulate a methodology for any forensic discipline. In doing so we must be careful, however, to not perpetuate the myth that there is a universal scientific method that applies to all scientific disciplines (and, therefore, to the discipline of bloodstain pattern analysis). In reality, the scientific method is better described by Percy W. Bridgman in his book Ref lections of a Physicist as “something talked about by people standing on the outside and wondering how the scientist manages to do it”. He then goes on to say, “Science is what scientists do, and there are as many scientific methods as there are individual scientists.”[7]
Although forensic examiners have been using sound scientific principles for years, these principles have not necessarily been presented in a concise and easy-to-understand manner. The same is true in the discipline of bloodstain pattern analysis. As analysts, we should be able to demonstrate the “scientific-ness” of our method without having to rely on that stagnant, yet mythical, scientific method proposed by those “people standing on the outside”. The eight-step process suggested in this article is not the only model that can be used by bloodstain analysts. What is important here is that the analyst devises some process that is (1) systematic, (2) based on scientific principles, and (3) easily articulated to judges, juries, and attorneys.
*From the Journal of Forensic Identification Vol. 55, No. 4, July/August 2005
The Official Publication of the International Association for Identification
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