Defining a Methodology for Bloodstain Pattern Analysis

Written By: Sam Savage

Published Date: July 19, 2006 Last Edited: July 19, 2006

By Gardner, Ross M

Abstract:

Articulating a Concise Scientific Methodology for Bloodstain Pattern Analysis [1] exposed and attempted to explain, in an easy- to-understand manner, the steps involved in reaching a conclusion. This article attempts to further explain the application of scientific method to bloodstain pattern analysis, detailing additional steps and the specific questions posed in that process.

Introduction

In an environment where lawyers routinely attack the tenets of every forensic discipline, it is absolutely imperative that students, instructors, and practitioners of the various disciplines know and apply functional methodologies. Although these methodologies may vary in minor ways across the spectrum of practitioners, the fact that individuals follow some form of established process enhances the probability that analysts (whatever their expertise) will stay a course and arrive at defensible conclusions. The use of a structured methodology helps limit much of the thunder from any lawyer’s attack of a discipline.

In the past, the discipline of bloodstain pattern analysis has suffered needlessly in terms of reputation within the legal system. In many ways, bloodstain pattern analysts have been their own worst enemy. Examples include the failure to define an effective taxonomy for bloodstain classification which has resulted in unnecessary ambiguity and the fact that too often students leave a basic course reciting only three phrases (“low”, “medium” and “high velocity”) and then fail to understand the application of these classifications fully. Worse yet, in documents written for defense counsel, individuals purporting themselves as experts in the area of bloodstain pattern analysis have literally claimed the discipline as subjective, writing: “Seen in this light, blood stain analysis is more of an art than a science and is always open to interpretation.”[2]

How is it possible that a discipline with a 150-year consistent history can be labeled an “art” and suffer from such issues?

The answer in large part is attributed to a published methodology, or lack thereof. Methodology is not taught in most bloodstain pattern analysis courses. Budding analysts are taught all of the skills applied in bloodstain pattern analysis: recognition of patterns, impact angle determination, and area of origin determinations, to name a few. But few instructors teach students how to apply these skills by providing a methodology that would keep the analyst within the confines of the discipline and help him or her reach valid conclusions. This results in analysts’ being unable to explain how they “analyzed”, which leaves the legal profession perceiving the discipline as without foundation. If the rank-and- file analyst cannot explain how he or she goes about the analysis, then how can the discipline hope to escape being labeled unscientific? The problem is not a lack of procedure, but rather a failure to articulate that procedure.

When pressed on issues of procedure, analysts routinely cite the use of scientific method; some even point to the ACEV technique as a functional methodology. Although valid statements, the discipline has failed to effectively describe how to apply these broad concepts when approaching the bloodstained crime scene. Articulating a Concise Scientific Methodology for Bloodstain Pattern Analysis [1] was an excellent start toward resolving this problem. Saviano put forth an eight-step process: (1) data collection, (2) case review, (3) isolation/description of patterns, (4) formulation of hypothesis, (5) testing of hypothesis, (6) formulation of theories, (7) testing of theories, and (8) conclusions and results [1]. But even this excellent article fell short in one important area: the isolation and analysis of the individual patterns, which is the key to all subsequent effort.

As a discipline, bloodstain pattern analysis purports to define “information specific to the events that occurred during the [bloodshed] incident” using information derived from “dispersion, shape, volume, pattern [characteristics], the number of bloodstains, and their relationship to the surrounding scene” [3]. Individual pattern recognition and analysis is the core of bloodstain pattern analysis and thus it must follow scientific method as well; but what does that really mean?

Scientific method, research method, whatever one might call it, seeks to answer specific questions using a standard process. As Saviano explained, the specific articulation of the steps of scientific method varies from author to author [1]. At its core, no matter who the author is, scientific method relies on an ability to define discrete objective questions, seek and find answers to those questions, and ultimately apply the answers from those questions to solve larger more complex questions. Posing and answering questions is the heart of scientific method, which begs the question. What should be asked in bloodstain pattern analysis? The ultimate question of bloodstain pattern analysis is, How was this stain created? To achieve an answer, the analyst must first ask and answer a number of far more discrete questions.

Application of Scientific Method to Bloodstain Pattern Analysis

In some fashion, instructors of bloodstain pattern analysis must articulate a process of what to do and in what order, associating it to the more philosophical aspect of scientific method. If the student of bloodstain pattern analysis docs not know what questions to ask and in what order to ask them, how then can he or she apply scientific method? A practical approach that resolves this problem can be articulated in seven steps. The bloodstain pattern analyst should:

1. Become familiar with the entire scene.

2. Identify the discrete patterns among the many bloodstained surfaces.

3. Categorize these patterns based on an established taxonomy.

4. Evaluate aspects of directionality and motion for the pattern.

5. Evaluate angles of impact, points of convergence, and areas of origin.

6. Evaluate interrelationships among patterns and other evidence.

7. Evaluate viable source events to explain the pattern, based on all of the above [4].

These steps effectively solve the issue of what questions need to be asked in bloodstain pattern analysis. Consider what these seven steps entail and the questions associated with each.

Step 1 – Become Familiar with the Entire Scene

This step involves the most basic questions posed in crime scene processing and crime scene analysis: What is the extent of the scene? What is present in it? If the analyst only considers certain areas, he or she may be missing critical stains or evidence. One never begins any type of scene analysis without first assessing the limits of the scene and knowing generally what is contained within it. Before any other action, the analyst seeks to familiarize himself or herself with the scene using whatever means are available. This entails many of the actions Saviano described in his steps 1 and 2 [1].

Step 2 – Identify Discrete Patterns

Bloodshed often involves multiple events that are ongoing in an area, resulting in stains that are deposited on or around other stains. For instance, multiple blows from a weapon may deposit impact spatter in several iterations onto the same surface, with limited movement of the victim. Or spatter from a cast-off event may occur simultaneously with impact spatter. These patterns tend to merge, making it difficult, if not impossible, to distinguish between them.

In this second step the analyst answers simple, but often elusive, questions: Where are the patterns that I intend to evaluate? What stains belong together? Consideration of the individual stain’s size, shape, position, and directionality are all aspects that help the analyst determine what stains will entail a pattern. Saviano offers this action as a part of his step 3. which he combined with classification [1].

Step 3 – Categorize the Patterns

This is the core step in bloodstain pattern analysis. The questions are, What kind of stain is this? Is this contact or spatter? Is it impact spatter or projected spatter? To answer these questions, the analyst must first have established criteria with which to compare the stain. Note that definitions abound in bloodstain pattern analysis, but definitions are not the same as criteria. For example, a definition of a cast-off stain as “a stain created when blood is flung or projected from an object in motion or one that suddenly stops some motion” does nothing to explain what characteristics were used by the analyst to conclude that the stain was cast-off in the first place. Besides articulating a methodology, the greatest difficulty affecting bloodstain pattern analysis today is the lack of a standard taxonomy.

A taxonomic classification system articulates the physical characteristics (e.g., shape, size, volume, number, dispersion, orientation) that must be present according to the analyst, in order to define something as belonging to a particular classification. In the example of the cast-off, these characteristics might be articulated as:

* a series of circular or elliptical stains (stains resulting from blood in free flight)

* that are positioned in a linear or curvilinear orientation

* with individual stains that have consistent direct\ional or gamma angles to the path of overall pattern.

The failure to teach and use an established taxonomy is why many analysts seem to believe that bloodstain pattern analysis is open to interpretation. If the analyst has no established criteria to look for before assigning a stain to a classification, then, in effect, any stain can be claimed as anything, by anyone. Even though the discipline has yet to create a standardized taxonomy, nothing prevents the individual analyst from having his or her own taxonomy or, at the very least, being prepared to describe his or her idea of these specific criteria. From analyst to analyst, some aspects may vary, but the basic idea of what creates a cast-off, an impact pattern, or a projected pattern is generally understood even if it has not been articulated well in the references.

Classification is the true key to successful objective analysis. Before the analyst can ever begin to consider a hypothesis in the context of the crime, he or she must know what kind of patterns he or she has. As Saviano pointed out, the focus is on the pattern itself with no attempt to infer the broader meaning of the pattern in the context of the scene [1].

These first three steps are accomplished in sequential order. The analyst first familiarizes himself or herself with the entire scene, so he or she knows where all the bloodstains are. The analyst then attempts to distinguish discrete patterns among the various bloodstained surfaces. Once this is accomplished, these discrete patterns may be categorized using a viable (physical characteristic- driven) classification system. Steps 4 and 5 follow and are accomplished as needed and in varying orders, depending upon the situation.

Step 4 – Evaluate Aspects of Directionality and Motion for the Pattern

In this step, the questions are relatively simple: From which direction did the stains being considered originate? What path were they traveling when they were deposited? Information of this nature will be significant at later stages when considering the flow of events and actions in the crime scene. Evaluating directionality is an integral step in establishing area of origin for impact spatter patterns, thus it is often evaluated simultaneously with Step 5. Nevertheless, direction and motion are not solely issues for spatter patterns; various drip, contact, and flow patterns require this consideration as well.

Step 5 – Evaluate Point of Convergence and Area of Origin

Using the mathematical techniques taught in basic a nil advanced courses, the analyst asks and attempts to answer questions relating to impact spatter: Can an impact angle be determined for this stain? If so. what is it? Is there a point of convergence for a group of related stains? C’an the area of origin be defined? If so, where is it? Although the importance of the mathematics of bloodstain pattern analysis is often overstated (most analysts spend less than 10% of their time evaluating these considerations), the answers to these questions can weigh heavily on the ability to evaluate a subsequent hypothesis about where these events occurred.

Step 6 – Evaluate Interrelationships among Patterns and Other Evidence

In this step, the analyst begins to look at the patterns in relation to one another and in relation to other items of evidence. In Step 3. the perspective was on the individual pattern under scrutiny. Here the analyst looks at the scene with a broader perspective. The questions posed include but are not limited to. Are these stains related? Are they the result of a common bloodshed event (e.g., a cast-off emanating from a spatter pattern)? Do patterns on loose items of evidence suggest a specific orientation at the time of the event? Is there evidence of sequence between different stains? Are a number of patterns present on different surfaces actually a single pattern (e.g., impact spatter dispersed over a wall and floor)? Consideration and refinement of these answers will often alter initial conclusions made in Step 2.

Step 7 – Evaluate Viable Source Events in an Effort to Explain the Pattern

Using all of the information derived from the analysis in steps 1 through 6, the stains and patterns must be considered in the context of the scene and incident in an effort to answer. What happened and in what order did it happen’.’ This final step effectively leads us back to Saviano’s steps 4 through 8, where the application of scientific method is directed at the broader investigative issues. Saviano eloquently described how the analyst moves from individual hypothesis to larger more encompassing theories, testing each objectively along the way [1]. This step may entail empirical experimentation in an attempt to determine whether a specific event or event sequence can re-create stains similar to those observed. Thus, the bloodstain data defines conclusions about specific events and, through an understanding of individual events, theories of what happened can be formulated and tested.

Conclusions

Despite all that has been written on bloodstain pattern analysis during its 150-year history, many in the legal profession continue to deride the discipline as unscientific and without objective foundation. Such misinformation is furthered in its cause by a failure of this discipline to adequately prepare rankand-file analysts to either conduct or explain bloodstain pattern analysis using a structured practical approach. And for those who do follow a structured process, as good as they are, many are simply not prepared to articulate that approach to the court. This has to change.

A practical systematic procedure or methodology is the basis of any good analysis. It should be taught and adopted at the most basic stage of bloodstain training and reinforced over time. The use of such a methodology ensures that the bloodstain pattern analyst follows accepted procedure in day-to-day activities. It does not guarantee the outcome, but lacking a methodology can certainly affect the validity of any conclusions drawn. The specifics of how that methodology can or should be written are debatable. As Saviano explained, which procedure is adopted is probably a moot point, as they will all follow a similar path [1]. But introducing a basic procedure into all bloodstain pattern training is a must. And once trained, every bloodstain pattern analyst should be prepared to effectively describe these steps to the court.

Received September 19, 2005; accepted November 22, 2005

References

1. Saviano, J. Articulating a Concise Scientific Methodology for Bloodstain Pattern Analysis. J. For. Ident. 2005, 55 (4), 461-470.

2. Akin, L. Interpretation of Blood Spatter for Defense Attorneys and Investigators: Part I, The Champion, May 2005, 26.

3. Bevel, T.; Gardner. R. Bloodstain Pattern Analysis With cm Introduction to Crime Scene Reconstruction, 2nd ed.; CRC Press: Boca Raton, FL, 2002; p 2.

4. Gardner, R. M. Practical Crime Scene Processing and Ivestigation; CRC Press: Boca Raton, FL, 2004; pp 267-268.

Ross M. Gardner

Gardner Forensic Consulting

Lake City, GA

For further information, please contact:

Ross M. Gardner

Gardner Forensic Consultirm

905 Windmill Court

Jonesboro, GA 30236

gard ner [email protected]

Comments

comments