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Crime Scene Analysis FAQ
What is Crime Scene Analysis?
Crime scene analysis, or crime scene reconstruction, is the process of evaluating the entire physical evidence and scene context in an attempt to establish specific actions that occurred during the incident under investigation. The analyst then attempts to order or sequence the events in question.
Is Crime Scene Analysis an established forensic discipline?
Crime scene analysis has existed as long as the concept of professional criminal investigations. This process has been discussed in various authors’ criminal investigative text over the last one hundred years. Edward Oscar Heinrich articulated a specific theory for crime scene analysis in the 1930s. This theory states simply that, “Nothing Just Happens”.
Are there defined principles or methodologies to use in CSA?
The history of crime scene analysis has recurring themes. These themes set forth a functional approach to the discipline of crime scene analyzing. There are several methodologies; BGA employs the method known as Event Analysis. All of the various methodologies are supported by several basic principles, which include: Steno’s Law of Superposition, Steno’s Law of Lateral Continuity, the concept of Chronology (both absolute and relative) and Locard’s Principle of Exchange.
Is Crime Scene Analysis synonymous with Behavioral Analysis?
Crime scene analysis and behavior an analysis are not synonymous, however, the latter employs crime scene analysis. Criminal profiling or behavioral analysis attempts to define aspects of the offender. The analyst must evaluate the physical evidence and scene in an objective fashion. Appropriate crime scene analysis is a necessity to the success of behavioral analysis.
How is Crime Scene Analysis used?
Beginning by first defining specific objective actions where the incident occurred, then sequencing those actions. The analyst sets an objective standard, which any theory or statement offered about the incident can be compared to. Investigative, prosecution and defense theories regarding the crime scene facts must functionally match up to the analysis. If the information is not synonymous, the theory must be re-evaluated and changed. Crime scene analysis can be used to refute or corroborate testimonial evidence when offered.
Bloodstain Pattern Analysis FAQ
What is bloodstain pattern analysis (BPA)?
Bloodstain pattern analysis, (also referred to as blood spatter/splatter analysis) is an in depth evaluation of the physical bloodstains found in a given scene. This evaluation is directed at three areas, pattern recognition and classification, the spatial origin or orientation of particular stains and patterns when created (e.g., flows or Area of Origin decisions) as well as aspects of alteration of the stain as a function of environmental exposure (e.g., coagulation times, drying times). The primary focus of the discipline is pattern recognition. Various pattern types are discerned by the analyst based upon the physical characteristics present in the unknown scene pattern. The analyst accomplishes this using a criteria based approach, in which physical characteristics of known pattern types are compared to the unknown scene patterns. To reach this conclusion the analyst considers a number of factors related to each pattern, including but not limited to: number, dispersion, shape, size, volume, orientation, and location. This classification of the pattern (e.g., spurt, cast-off, swipe) defines the basic nature of the physical action that created it. Once this pattern classification is identified, it is then considered in the specific context of that unique crime scene (e.g., consideration of whose blood is present and what injuries or mechanisms were in play in that scene) which ultimately defines the events that occurred or did not occur during the incident.
What do you mean by basic nature?
Blood as a fluid is affected as all fluids are by associated physical laws (e.g. the effect of air resistance, gravity, surface tension). If we expose a mass of blood to a basic event (e.g. striking it, streaming it under pressure) the resulting pattern will demonstrate particular characteristics. Thus bloodstain patterns are reproducible phenomena. Although various classifications systems exist to explain the resulting patterns, within all of these systems are basic pattern types. In one form or another, these will include:
- Disruption of blood at a point source (radiating spatter patterns)
- Dispersion of blood over time and space from an object in motion (castoff patterns)
- Dispersion of blood from a point source as a stream under pressure (projected patterns)
- Gravity induced patterns (drip patterns)
- Stains resulting from contact (contact/transfer patterns)
- Volume patterns (pools, flows)
What is the goal of the bloodstain pattern analyst?
The goal of the bloodstain pattern analyst is to recognize this basic nature of the stain through these physical characteristics, properly classify the pattern and then to associate the pattern back to a source event within the context of the scene. This final step is a function of associating the pattern to a specific event that occurred during the incident in question.
For instance: In a scene we might find a radiating pattern of very fine spatter deposited on a surface in close proximity to a bullet defect. The autopsy information advises us that the victim received a perforating gunshot wound. DNA testing verifies the blood is that of the victim. Using BPA the pattern would be recognized as an impact spatter pattern. The small (sub-millimeter) size of the stains in the pattern might suggest explosive force and thus the analyst could functionally opine that the pattern was produced by the gunshot event.
Can BPA always associate a pattern to a specific source event?
No. Bloodstain pattern analysis is class characteristic type evidence. This ability to associate a specific pattern to a specific source event is the goal of BPA, but it is not always feasible. We can generally identify the basic type of pattern, but it is only through scene context that we can ultimately associate it to a specific event. It is not uncommon that the analyst will recognize that a particular type of pattern is present, but not be able to limit it to a specific event.
For instance: In a case involving multiple blunt trauma blows delivered by both hands and a weapon, the analyst would certainly recognize the presence of multiple impact spatter patterns. But it is unlikely based only on the spatter patterns themselves that the analyst could associate one pattern to a particular blow by a particular weapon.
Why are there so many blood spatter analysis classification systems?
In BPA there are various systems of classification. Each developed in its own right and each has value and function. Over time different professional groups and different teachers adopted different systems. Although on first glance it might seem as if they are disparate systems; as previously discussed inherent in all of these systems are the basic pattern types. The systems simply start from different initial perspectives. Examples of different classification systems include:
LVIS, MVIS, HVIS. This system concentrates on the idea of spatter size as a principle distinction. Although well known, for various reasons associated to misuse and misunderstanding, this system is being replaced by other classification systems.
Passive/Dynamic. This system is mechanistic and starts with the nature of the underlying event. Dynamic patterns are those associated to disruption mechanisms (e.g. impact, castoff, projected). Passive patterns are contact stains and patterns produced by gravity.
Spatter/Non-Spatter. This system is taxonomic in nature. The principle starting point is whether the pattern is made up of droplets that have been in free flight (small stains circular or elliptical in nature). Spatter groups include impact spatter, arterial spatter, castoff stains, and drips. The non-spatter include pools, flows and stains produced by contact.
Is BPA a science?
The Bloodstain pattern analysis (BPA) is the scientific study of the physical properties of blood in motion and the static aftermath resulting from dynamic event(s) involving bloodshed. As an applied science, BPA draws upon the related fields of biology, chemistry, physics, and mathematics. It involves detecting, documenting, describing, analyzing, and evaluating, of bloodstain pattern(s) specifically the size, shape, distribution, number, and location of bloodstains, as well as the nature of their target surfaces along with their interrelationship(s).
Active areas of research in the field of BPA includes studies of the physical properties of blood, synthetic blood substitutes, the formation of drops by the action of external forces, blood drop behavior in flight through air, interaction of drops and transferred blood with various surface materials, and blood drying and the appearance of dried stains. In current practical application, BPA is usually applied to observed and documented patterns by applying knowledge obtained through research efforts in determining probable mechanisms of stain or pattern formation.
What is the methodology of BPA?
Different analysts may represent their methodology in different fashions. We describe it as seven steps. Following scientific method, each step asks and answers specific questions. Of course the ultimate goal is to try and associate a pattern back to a specific source event. As we teach methodology these steps include:
- Assess and familiarize yourself with the scene.
- Identify discrete patterns.
- Classify the patterns.
- Consider directionality and motion.
- Consider points of convergence and area of origin if necessary.
- Evaluate interrelationships between patterns and other objects.
- Evaluate and identify viable source events, if possible.