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The science of BPA (Blood Stain Analysis) applies the knowledge of science from other disciplines in analyzing and solving crime related problems. Blood Pattern Analysis applies knowledge from chemistry, biology, mathematics and physics in analyzing blood stained crime scenes. This excerpt therefore aims at analyzing and outlining the basic precautions that ought to be taken by crime scene technicians and investigators in handling blood as well as the other biological fluids found at a crime scene. This article also discusses how evidence from bloodstain found at a crime scene can be used to provide crucial information on the type and sequence of events at the crime scene. Such analysis at the crime scene is supported by the Locard’s principle which states that the perpetrator will always take away traces of the crime scene and the victim while the victim will always retain traces of the perpetrator. The principle also adds that the victim will in most cases leave traces of him/herself on the perpetrator and the perpetrator will leave at the crime scene traces of himself/herself in several ways. This principle is then applied in the evaluation and retrieval of information from a blood stained crime scene.

The article also aims at explaining how the crime scene is processed so as to retrieve bloodstain pattern evidence by use of bloodstain classification. The article also addresses the classification of stains by using concentration, location and distribution. Classification enables the analysts to define a source event for any given stain at the crime scene. Blood stain analysis has been a very useful tool for the crime investigators in defining the type and level of seriousness of a crime and the evidence has also helped in arresting the perpetrators.


BPA (Bloodstain Pattern Analysis) is one of the many specialties in the field of criminology and forensic science. According to Gardner (2005), bloodstain evidence has been in use for a very long time. However this evidence has been brought to a much higher level by the application of modern science. New technologies such as DNA analysis are currently being used by criminologists and detectives in apprehending offenders and solving crimes. The science of BPA applies knowledge from other scientific fields to analyze blood stains. The analysis draws from other disciplines like physics, chemistry, mathematics and biology. According to Geberth (2007), when the recommended scientific process is followed, this applied science of bloodstain pattern analysis can give substantial and solid evidence hence making it an effective tool for the crime technicians and investigators.

In bloodstain pattern analysis, the investigators are usually required to have a fundamental understanding of blood spatter analysis to enable them collect and preserve bloodstain data correctly from the crime scene. When the investigators and the first responding officers know what they have at the scene, they should then know what to do next basing on their department policy. According to Gardner (2005), bloodstain pattern analysis requires enough training and education so as to be an effective technique of investigation. However this technique is not usually present in all the law enforcement officers or investigators attending a crime scene. Blood stain analysts undergo a specialized training which is usually offered in many private and government institutions.

Bloodstain Pattern Analysis is generally new within the recognized disciplines of science and therefore objective and subjective approaches presently subsist in casework training and adjudications. Bloodstain pattern analysis is now frequently included in training programs, science presentations, and in new publications of forensic science. This indicates therefore that readers are interested in gaining more information regarding the investigative potential of bloodstain pattern analysis which is probably the oldest form of physical evidence in history (Wonder, 2007, p.3). Over the recent past, forensic science emphasis has concentrated on standardization. With specialties such as fingerprints, DNA, drug assays, fibers, firearms and tool marks, standardization is important and straight forward to plan. Complete standardization could be harder to define with bloodstain pattern analysis because of the discipline’s scope. Areas involved in this discipline include bloody transfers, spatter events, coagulation information, bloody transfers, medical would and injury reports, flows with drying, fire arm dynamics, flows with drying, legal preparations, public opinions, photography and various technical subjects like colloidal chemistry, mathematics and engineering principles among others (Wonder, 2007, p. 5).

Regarding standardization of certain aspects of bloodstain pattern evidence, it may be currently too early since the most recent scientific discoveries regarding the behavior of blood have not been integrated into understanding the discipline at this point in time. Moreover, currently the ultimate decision as to whether the evidence will be used in investigations and in court adjudications lies with the law enforcement officers and not with the science professions. However subjective application may sometimes be favored over objective applications when the evidence is presented in court. It would therefore be a mistake to standardize principles at a time when subjectivity may prevail.

Bloodstain Pattern Analysis and interpretation is one of the most explicit methods of forensic science that illustrates its reconstructive nature in the analysis. According to Houck & Siegel (2010), BPA (bloodstain pattern analysis) is defined as the analysis and interpretation of shape, dispersion, shape characteristics, pattern, volume, number and relationship of bloodstains at a crime scene to reconstruct a process of events (p.244). BPA is also defined as the science of examining and interpreting blood found at a blood shed event with an aim of finding out the events that took place, their order and possibly know who left the stains. Bloodstain pattern analysis needs a combination of physiology, physics, geometry and logic (Dutelle, 2010, p.237). The patterns present, the volume of blood, dispersion, shape characteristics as well as number of characteristics present at the scene are all put into consideration during the evaluation and analysis. However BPA is not the sole answer to all the questions concerning what took place at the scene but it’s instead a tool within the bigger toolbox of crime scene investigation. Everyone in this field is required to undergo an extensive training together with a solid scientific education before he or she can participate in bloodstain pattern analysis.

History of Bloodstain Pattern Analysis

Just like the track impression evidence, the historic origin and development of BPA (Bloodstain Pattern Analysis) is believed to date back from the early man’s hunting efforts. The document of Paleolithic art explains the skills of the early human hunters and shows how they used blood tracks to locate prey. According to Dutelle (2010), biblical passages associate bloodstains with mortality and injury (p. 238). It’s therefore reasonable to conclude that human beings have been analyzing bloodstain patterns for more than 4,000 years. According to Dutelle (2010), investigators have been trying to analyze bloodstains since the start of criminal investigations, though bloodstain analysis as a unique area of crime scene investigations and forensic science appears to be more of a modern occurrence (p.238).

This science got into higher levels during the early 1900 when a number of prominent scientists and scholars started researching and experiment on blood dynamics and on human blood properties. Though a number of people recognized the essence of such matters, historically bloodstain pattern analysis as a forensic science is credited to Dr. Paul Leland of the University of California (Dutelle, 2010, p.238). Dr. Paul was recognized when he provided evidence using blood and pattern evaluation in an effort to explain what took place at the home of Samuel H Sheppard leading to the death of Sheppard’s wife in 1955. This case together with Dr. Paul’s textbook on crime investigation is regarded as an impetus for the today’s forensic study of BPA. After this incident however, the number of authors and scientists writing on bloodstain analysis began to increase in tremendous manner. One of these authors was MacDonnell who is recognized for reawakening the discipline and for providing the psyche to professional organizations like the IABPA (International Association of Bloodstain Pattern Analysts) and the IAI (International Association of Identification), to begin offering professional training and certification in this field. Following this professional and academic development, the entire discipline has gained enormous acceptance as a source of evidence in courtrooms within the United States and across the world.

Properties of Human Blood

According to Dutelle (2010), a normal and a healthy adult human being has approximately four and half to six liters of blood in his or her body (p.239). Noting the amount of blood found in human beings is very crucial for an investigator since if there appears a larger volume of blood at a crime scene than what a single human being can produce, then the evidence would either suggest that the injury resulting in the bloodshed was not in line with sustenance of life, or that the blood present was from several individual. When subjected to external forces, blood will always act in a manner that can be predicted (Dutelle, 2010, p.239). Scientists have also found out that the surface tension of blood is a little lesser than that of water and that blood falls in a spheroid configuration and not in a ‘tear drop’ as its typically drawn and shown. The volume of an average or a typical drop of blood is measured to be about 0.05 milliliters and with and average of 4.56 mm in diameter while in air (Dutelle, 2010, p.239). The higher the viscosity of a fluid, the lower its flowing speed. In this context, experiments indicate the blood is six times more viscous than water and that it has a specific gravity slightly higher than that of water.

Deeper studies on the properties of blood show that bloodstains dry from their outside perimeter and inwards toward the center. As the outside margins of the stain dries, it becomes more resistant to removal or disruption than the wet interior part of the stain. Generally, a minimum of one minute is required for a bloodstain to form a dry perimeter. However since the drying period or time of blood is dependent upon the surface on which it’s deposited, the volume deposited and the environmental conditions its subjected to, this drying interval may therefore be experimentally determined according to the discretion of the BPAE (Blood Pattern Analysis Expert) (Dutelle, 2010, p.239). The above mentioned blood characteristics are what is followed by the blood analysts in the subsequent interpretation of bloodstain pattern at the crime scene.

Blood Pattern Interpretation

According to Dutelle (2010), the ability to construe a bloodshed event should considered as a forensic tool that aids the crime scene investigator to understand better what happened and what could not have happened during a bloodshed event (p.239). Information obtained from a crime scene can be used in corroborating a witness’s statement, in apprehending a suspect, in interrogating a suspect, in reconstruction of event or can also be used to acquit an accused person. By careful examination and evaluation of the physical evidence, the investigator is able to deduce certain information regarding the events that took place during the bloodshed event. Generally the crime scene investigator observes three main areas concerning the bloodstains when putting together his/her findings and conclusions. These three areas are the shape, size and distribution of the bloodstains. These aspects are each examined separately and their findings combined so as to give information that is specific to the event.

Bloodstain Shape

One of the main sources of information possessed by a bloodstain is its shape. Careful and extensive analysis of the blood stain shape allows the crime scene investigator to tell the direction from which the blood originated (Dutelle, 2010, p.240), which can be very beneficial in assisting the crime scene investigators understand what took place at the crime scene. Directionality is wholly determined by only looking at the shape of the bloodstain. It has been found that the narrow end of an elongated bloodstain will typically point in the direction of travel for many stains, specifically those deposited on non porous surfaces it is possible to deduce the direction in which a drop was moving by comparing the edge characteristics in the two extreme margins of the stain. That distal margin of the bloodstain which shows lesser disruption with respect to its opposing margin is what was deposited first. On the other hand the margin that displays or shows the greater disruption is the one that was deposited second (Dutelle, 2010, p.240). This way, a bloodstain can be said to have a directionality that tracks along the path of its long axis and in the direction that encounters its edge of lesser disruption long axis and in the direction that encounters its edge of lesser disruption first and the edge of greater disruption next.

However the information deduced from the shape of a bloodstain does not end there. When a blood source is impacted or subjected to substantial force, blood droplets are usually projected upon target surfaces at various angles of impact. In such a situation, if the investigator was to draw an imaginary line through the long axis of each bloodstain in the direction opposite of the observed travel they would arrive at a two-dimensional point known as an area of convergence. However this is a two dimensional explanation and that it does not explain how far from the area that the blood event originated. Instead this explanation gives an area in which to determine such information. For instance once the area of convergence within a room has been found out, in order to determine the origin distance from the floor or wall within that room, a third dimension needs to be considered.

By establishing the impact angles of representative bloodstains and projecting their trajectories back to common axis (Z) extended at 90 degrees from the intersection of X and Y axis, an approximate location of where the blood source was when it was impacted may be established. However so as to locate this, the examined blood needs to be analyzed to determine its angle of impact.

Angle of Impact

When adrop of blood impacts a surface at an angle of 90 degrees, the resulting bloodstain will generally be circular in shape. Blood droplets that hit a target at angles less than 90 degrees will create bloodstains that are elliptical in shape. Although this is helpful in approximating the origin of a bloodstain, the crime scene investigator is able to gain a much closer approximation when he applies the mathematical relationship that exists between the length and width of a blood stain (Gardner, 2005). This relationship allows for the calculation of the angle of impact for the original spherical blood drop.

In calculating the angle the investigator must first take measurements of the length and width of the bloodstain being analyzed. The width of the bloodstain is then divided by its length. It’s also important to note that when measuring the length of a bloodstain one should not include the tail portion of the stain (Dutelle, 2010, p.243). Inclusion of these tail ends in the measurement of length leads to underestimation of a stain’s impact angle. After these measurements the crime scene investigator should use a scientific calculator to compute the angle of impact of the bloodstain. The calculation of the angle is done by getting the arc sine or the inverse sin of the ration between the width and the length.  For instance, for a circular blood stain the length and the width are equal and therefore their ration is 1. After computing the inverse sine of 1 we get 90 degrees which is the impact angle of a circular blood drop.

After finding out the impact angle for each bloodstain, the 3-dimensional origin of the bloodstain pattern can be established. One of the methods used is placing strings at the base of each bloodstain and then projecting these strings back to the axis that has been extended 90 degrees up or away from the area of convergence. This is then followed by placing a protractor on each string and then lifting the string until it corresponds with the earlier determined angle of impact. This is then repeated for all the bloodstains analyzed.

Types of Bloodstains

As stated earlier an adult human being contains about 5 liters of blood. Loss of30% of this blood leads to incapacitation or unconsciousness while the loss of 40% of the total blood often leads to death. Its should however be noted that bleeding is usually external and internal and therefore the amount of blood surrounding a body may not reflect the actual amount of blood lost (Gunn, 2009, p.52).Blood from the arteries (except that from pulmonary artery) is usually bright red in color due to its high oxygen content while blood from the veins is darker in color since its deoxygenated. However, one outside the body, blood begins to darken and clots within approximately three minutes and therefore it’s hard to tell if the blood came from the veins or from the arteries. In this context still, there has been not methods of determining the age of dry bloodstains though studies on DNA composition have indicated some potential. Many studies group bloodstains as low, medium, and high velocity spatter based on their distribution, size, and the force necessary for their production.

These causes could be given as beating, dripping and shooting. This implies that the higher the velocity of blood drop, the smaller the bloodstain (Gunn, 2009, p.52). According to Dutelle (2010), all the bloodstains left at a crime scene can be grouped into passive, transfer, miscellaneous and projected/impact. This grouping was initially suggested by Jozef Radziki in 1960

Passive Blood Stains

These bloodstains consist of drips, clots, flows and blood pools (Dutelle, 2010, p.246). These stains are usually not associated to any specific action within the scene context and as regards to bloodshed violence. Instead these stains are associated with the aftermaths of the violence as the bloodshed begins to move and cure due to gravitational and environmental forces.

Drip (Blood in Blood)

Drip patterns come from blood dripping into another blood. These patterns generally show satellite staining which results from deposition of small droplets which are ejected from a pool of blood when an object falls on it. Since these ejected droplets of blood usually follow arching trajectories, they are found to strike the surface at 90 degrees resulting to circular and near circular stains. Moreover, since these stains are generally slow in motion, the satellite stains around the central pool of a drip pattern often show a noticeable thickness since their droplets don’t have the necessary energy to spread themselves fully over the target surface when they strike it (Gardner, 2005, p.147). The satellite stains found on the outside margin of a drip pattern on a vertical surface usually show evidence of gravity effects. These stains also show directionality towards the horizontal surface since the deposited droplets were on downward flight path of their travel arch. On the other hand the size of the satellite stains on a vertical surface will usually decrease as the space from the blood pool that resulted in the drip pattern increases.

Single blood drops will display small spatters around the mother stain due to their striking of a rough surface and this is referred as secondary spatter. When several free-falling blood drops are produced from a stationary source, onto a horizontal surface, particular drip patterns that are large and irregular in shape will result.

Flow patterns

These are the change in shape and direction of bloodstains due to the movement of the surface and influence of gravity. These flow patterns are usually seen in situations where a volume of liquid blood moves freely along a downward path. These flow patterns may sometimes also show more than one long and narrow stains that may be originating from a distinct bloodstain pattern. A flow pattern that does not extend downwards on the surface as observes shows that the object or surface was moving during blood flow or that the surface was moved after the blood flow had stopped.


Clotted blood is defined as a “blood that has undergone the physiological process of fibrin formation that congeals the solid element of blood into a gelatinous mass” (Dutelle, 2010, p.247). Blood shed from the body in enough volume to remain liquid for longer period of time may show clot formation. The minimum amount of time necessary for clot formation to start, ranges from three to fifteen minutes.  This time however depends on many factors including blood volume, surface deposited and environmental conditions. Large pools of blood that collect on non absorbent surfaces can remain liquid for an enough period of time to display clot formation. Other blood pools that undergo blood formation clot formation usually show large gelatinous masses with serum collections in the peripheral margins of the blood pool. On the other side individual stains that show clotted material may be produced when blood that has already clotted is subjected to disruption by a force. Such stains may show a central region of dense staining that is surrounded by a ring of less dense staining.

Transfer blood stains

Transfer blood stains also called contact patterns, are generally indistinct stains that can be of any shape or size. The physical appearance of these stains is usually mottled with several variations in color and density. The shape of a transfer or contact pattern may retain some physical characteristics of the object that created it. This way the shape of a transfer pattern can therefore be used to tell or suggest the object that created it through the recognizable patent image (Gardner 2005 p.146). The direction of motion of a contact pattern can be deduced from the general density distribution of the stain.

Generally a transfer or contact bloodstain pattern is heaviest in the portion of stain that is deposited first and then its density decreases as blood is removed from the object. According to Dutelle (2010), feathered margins may be created as the object eventually looses contact with the target object. The presence of unique front boundaries deposited along the margins of a transfer/ contact pattern can also be used in the determination of the direction of movement. These front boundaries result from the blood that collects along the leading edge of an object. Since these front boundaries are left or found where an object loses contact with a surface, they are therefore more numerous in that part of the stain deposited last.

In bloodstain pattern analysis there is also a phenomenon called swipe. A swipe happens when a bloody surface rubs across a non-bloodied surface. This phenomenon is beneficial to the crime scene investigators as it gives some information about the movements within the scene. In a swipe there is usually an initial point of impact which leads towards a disappearing or feathered edge. Normally the movement will be towards the feathered edge. Apart from a swipe there is also a wipe which occurs when a non-bloodied object or surface moves across a stationary bloodied surface. The pattern produced in such a case is also very important since it gives the crime scene investigators a clue about the movements at the crime scene. We also have the pattern transfer which occurs when a blood wet object comes into contact with a secondary surface that is unstained. In this blood transfer pattern, a recognizable image of all or part of the original surface is observed in the pattern (Dutelle, 2010, p.250).

Projected blood stain patterns

Projected bloodstain patterns are produced when blood is released under high pressure for instance that blood released from the arteries. These projected patterns result from generally larger volumes of blood than those that produce other dynamic stains like the passive and transfer stains. When the trajectory of a bloodstream hits an obstructing target, a fairly large central stain is created and it’s usually surrounded by many spines of varying length. According to Dutelle (2010), the appearance of this peripheral staining may be useful to the crime scene investigators in accessing whether a volume of blood struck a surface or an object forcefully (p.250). Projected streams of blood that do not strike a vertical surface continue along individual parabolic flight paths until these streams deposit on a horizontal surface.

Cast off patterns

These are examples of projected bloodstains which are created when blood is thrown or released from a moving object that has blood. These casts off patterns can result from two situations. They can either be created when blood is released from an object due to the effect of centrifugal acceleration or can result from cessation instances or stop action, when drops of blood are thrown from an object when the motion of the object is stopped abruptly. In the first case, the pattern produced is known as Arc Cast-off Pattern where the individual stains are generally spread in a linear configuration and can be used in estimating the plane in space through which the bloodied object was moved. According to Dutelle (2010), by looking at the shapes of individual stains within the pattern it is possible to deduce the direction of travel of the object (p.251).

For the cessation patterns, the individual stains are generally smaller in size as compared to those resulting from passive blood drops. These stains are of various shapes. According to James, Kish, & Sutton (2005), cessation patterns do not generally display the linear arrangement of individual stains as in the arc cast-off patterns. Since cessation cast off patterns are produced as when a bloody object is abruptly stopped, then these patterns can be produced by one or more impacts received by a blood source.

Miscellaneous bloodstains

Miscellaneous blood stains are classified as void, skeletonized and insect spots. When there is an individual or item between the surrounding surfaces and the area of impact, then the object will create a void pattern upon the surrounding items or wall.  A void is described as an area that is absent of any projected blood. This pattern is mostly used in determining the shape and size of interfering objects. Insect spots are small bloodstains formed by insects when they step on clean surfaces after stepping of bloody ones (Dutelle, 2010, p.252). This category of patterns is included to cater for the activity of flies and other insects within the crime scene. Lastly when the center of a dried blood stain flakes away and leaves a visible outer rim, the result is what we refer to as skeletonized stain. A skeletonized bloodstain is also formed when the central part of partially dry bloodstain is altered by a wiping motion. 

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