Violent offences lead to the injuries which are accompanied by the blood flow.
The blood flow due to injury may results in the formation of pattern of blood stains.
These patterns give the extensive and investigative information related to the actions or activities occurred at the time of offence.
Blood stain pattern analysis helps in determining the direction of blood travelled, the location or position of source of blood, movement during and after bloodshed etc.
Analysis of blood stain pattern provides information about how distinct activities/movements and forces impacts the appearance and formation of the patterns of bloodstains.
It is a useful forensic tool in crime scene investigation.
Bloodstain pattern analysis is the examination and analysis of the distribution pattern, location, direction and shapes of bloodstains.
The examination or analysis of bloodstain patterns is mainly useful in providing elucidation of the physical events that gave rise to the origin of blood stain.
A detailed and extensive understanding of a dynamics of blood as well as formation of stain is a necessary prerequisite to the detailing interpretation of the spatter patterns as well as individual bloodstains.
BPA is a discipline or branch of forensic science which deals with blood’s physics and recognizes the stains of blood present at scene of crime by using recognition of visual patterns.
This method is useful in shedding light on several forensic matters such as event’s reconstruction etc. T
Here are various documented descriptions of shapes of the bloodstains present at a scene of crime that dates back to the past few centuries.
However, major advances in the field of bloodstain pattern analysis were evoked by the Samuel Sheppard case in United States of America.
Analysis of Bloodstain pattern is used by police officials, medics and scientists worldwide.
There are two things which are essential in the evaluation of the bloodstains are blood and surface on which stains of blood are observed.
IABPA stands for International Association of Bloodstain Pattern Analysts which is a main organisation for the analysts of bloodstain patterns. Several forms of memberships are offered by this organization.
Uses of Bloodstain Pattern Analysis
BPA stands for Bloodstain Pattern Analysis (BPA) which means it is a systematic assessment, evaluation or examination of the visual bloodstain patterns at a scene of crime which depends on physics of fluids.
The analysis of bloodstains depends on its size, shape, and distribution also. The main focus of this method is to answer the question that how a blood travelled through a specific space in orders to produce bloodstains on surface.
The analysis of bloodstain patterns is important in:
1. Reconstructing the events of an accident or offence
2. Statement verification
3. In cases which consists of doubt of involvement in an offence
4. Recognition of areas where the movement of perpetrator is high for the purpose of prioritisation of the samples of DNA
5. Differentiation or disparity in between an accidents and suicide/homicides
Analysis or examination of bloodstain patterns is mainly based on the principles of physics, as well as medical, chemical and biological knowledge or understanding.
Characteristics of Bloodstain Pattern Analysis
Size and Shape
The shape of the bloodstain represents the direction of travelling of blood and the angle at which the blood falls on the surface.
When the blood passively falls on a smooth and horizontal surface, the bloodstain pattern will be round.
The texture of the striking surface influences the shape as well as size of the bloodstain pattern.
Tough, hard or strong non-porous surface generates round stain patterns whose edges are smooth.
But, the soft and porous striking surface generates spatter stains whose edges are rough.
A drop of blood acquires an oscillating sphere’s shape, when it falls through the air.
Blood drops fall because of the gravitational pull and does not split-up in the air/atmosphere.
But additional forces, other than gravitational pull are able to break or split the blood drops.
Angle
On changing the angle of blood drop impacting a surface, the bloodstain shape will also change.
The pattern of bloodstain formed will be more elliptical, oval or elongated, when the impacting angle is small or more acute.
The determination of angle of impact of the blood drop can be done by measuring the length and width of the bloodstain.
The trigonometric relationship in between the ratio of long axis vs. short axis of a stain of blood (length vs. short axis) can be determined.
When a drop of blood falls vertically at a 90-degree angle, a round stain is formed. The blood drop gets elongated on increasing impacting angle and also a tail develops which is pointing towards the direction of travel of blood drop.
A drop of blood will be narrower and longer when struck a target surface at 12 degree angle.
Direction
The shape of bloodstain will demonstrate the travelling direction of blood. In general, the “tail” also known as “wave castoff” of the stain of blood indicates its travelling direction.
The travelling direction as well as impacting angle is known as the directionality of patterns of bloodstain.
The bloodstain directionality is helpful in reconstructing the location of bloodshed.
For example: when a drop of blood falls from a small distance, the bloodstain formation will be circular or round up to 45 degree angle.
When a blood droplet falls on a surface at a 90 degree, the circular bloodstain will be formed, due to which the length as well as width of the stain of blood will be uniform.
The formation of shape of the bloodstain will be teardrop or elongated, when a drop of blood falls on a surface at less than 90 degrees. The bloodstain’s diameter also increases, on increasing the distance of impact/fall until reaching a maximum diameter.
Volume
Bloodstain’s diameter also gets affected by the volume of blood drop.
The diameter of the stain of blood also increases, when the volume of blood drop increases.
A drop of blood falls off on a surface due to the increase in volume to the extent where the blood’s viscosity overcome by the gravitational pull of Earth and break the surface tension.
Force
Force is another characteristic or factor that affects the bloodstain pattern.
How much force applied on source of blood to put that into flight is also an important factor.
Some of the blood react and put it in flight, on imparting external force on the static blood.
The amount of blood drops put in flight is less, in low velocity events, but the droplet’s size will be large.
On increasing force, the diameter of a drop of blood decreases, with most of the drops of blood being 1mm (in diameter).
Distance of Fall
The diameter of drop of a blood decreases on increasing the force.
The distance travelled by a blood drop through the air is always dependent on the amount of force exerted to form a drop, air currents and size of the drop of blood.
The amount of drop of blood in flight is low in case of low force/low velocity events but the size or dimensions of the blood drops will be large.
The diameter of most of the blood drops will be larger than 3mm, but very few of them will be less than a diameter of 3mm. So, the distance travelled by these blood drops from the source of blood will be short.
The amount of drops of blood put to fly and the distance travelled by them from the source of blood will increase on increasing the level of velocity or force.
On increasing the impacting force, the blood drop’s diameter will decrease, with most of the total drops of blood having diameter of 1mm.
The distance of travelling by small blood drops is less due to the lack of physical weight for resisting the friction and air currents, but the energy responsible for forcing them in flight depletes rapidly.
Most of the blood drops which are small in size is not able to travel a distance of more than 3 ft. (0.9 m) from the source of blood.
Numbers of drops of blood will be put in the flight which are mainly = or <1mm in a diameter, in case the extent or degree of force becomes very high like spatter caused by gunshot.
The blood drop’s size will increase, on increasing the distance of travel from the source of blood.
Principles of Bloodstain Pattern Analysis
- A liquid blood drop acquires the shape of a drop only when it falls from an object. A minimal surface area is taken by the blood drop when it is air born and then moves in flight in a shape of sphere. There are several physical forces that act on blood droplets like gravitational pull and air resistance.
- Flow-patterns are caused by the gravitational pull/ force. The formation of Flow patterns are caused by the blood movement across a surface because of the impact of gravitational force.
- Large pools or amount of blood, results in separation of the serum such as on the solid surfaces. The fact is that RBC’s sink due to its weight but serum present on the surface as a transparent and clear liquid. Those peoples who are not familiar with this phenomenon thinks that a liquid has been added in the blood. But this is a non-exploited or manipulated pool of blood, in which the standing blood is present.
- There is one more difficulty or problem that distinct causes, in few cases, can results into stains that looks exactly identical. To overcome this issue, in-depth knowledge or understanding of physics as well as bloodstain patterns and differential diagnosis is important for formulating a precise assessment.
- It is important to note that the analysts also faced that conditions in which the bystanders are more stained with blood than the culprit. This happens in cases where a weapon/tool/object is oscillates overhead in a group of peoples. These types of cases are rare but also essential to consult with specialists.
Bloodstain Pattern Classification
The classification which is in use nowadays is of P. Kish, S. James and P. Sutton.
According to this classification, there are 3 categories:
1. Gravity/Passive Bloodstains
2. Spattered Bloodstains
3. Altered Bloodstains
According to the first category, the “passive bloodstains” are those bloodstain patterns which are developed under the influence of gravitational force.
This category consists of contact stains, which are formed by the contact between the two surfaces, out of which one of the surface contains blood.
These types of stains gives information about the sequence or series of movement. Drip stains, saturation/pooling and flow patterns also belong to this group.
The second category belongs to spatter. It includes those spatters which results from the active events like a shot, and also include spatter which are caused by cast-off or expiration from weapon or objects that oscillates.
All other types of stains like diluted blood or blood clots comes under the third category of bloodstains which results due to the incorporation of other type of liquids.
Bloodstain Pattern Analysis at Crime Scene
- As according to the principles of investigation in forensics, any trace found at crime scene should be secured in order of its sensitivity. Those bloodstains which are exposed to the environmental effects may need examination in a short time span. In order to evaluate the travelling of blood in a specified space, it’s essential to understand the location of the bloodstain. The analyst for analyzing bloodstains or bloodstain patterns visits the scene of crime. It is rare that evaluation is based on the photographs.
- It is necessary to assess area at crime scene that contains bloodstains and also those areas that do not contain any bloodstain. The bloodstain location gives indications about the area of action in a given location.
- The area of source of the spatter three-dimensional in the specific space can be calculated. It is dependent on the flight phase that the drops of blood are in. The blood drops shapes is dependent on the angle of impact on surface.
- It is essential to contact a bloodstain specialist in the initial investigation stages at a scene of crime. Other procedures are also performed additionally to the regular analysis, such as utilization of the forensic light sources, which is standard nowadays for detecting stains but chemical substances like Leucocrystal Violet/ Amido Black/ Fluorescin/ Luminol can be utilized for enhancing or detecting stains of blood.
- A preliminary or initial blood test is essential for establishing the existence of blood when such types of methods are employed.
- Thorough and preliminary documentation is necessary at a scene of crime where blood discharge occurs. It is suggested that the exposed parts of the cadaver such as outer and inner surface of hands should also be photographed along with the usual documentation process.
- It is also essential to take photographs of the clothing. At the time of transport, it is possible to lose the stains of blood present on the body surfaces. At a time of transporting cadaver, it is possible to lose various information regarding the position and movement, in case when unsecured evidences is abandoned on body of cadaver.
- All the photographs of scene of crime are essential while preparing a report.
- Essentially, the report of an expert contains descriptive section, which includes the description of the bloodstains and analytical section, which contains the details about the bloodstain evaluation. It is also important that the expert must give an opinion about the surface which contained stains of blood and also, the state of blood. It is also essential to consider the state as well as type of the surface. Contrast as well as surface structure also plays an essential part.
References
Bevel, T. /Gardner, R. M. (2008). Bloodstain Pattern Analysis, Boca Raton et al.
Brodbeck, Silke (2012). Introduction to Bloodstain Pattern Analysis, SIAK-Journal − Journal for Police Science and Practice (Vol. 2), 51-57.
Craig D. Adam, Fundamental studies of bloodstain formation and characteristics, Forensic Science International 219 (2012) 76–87.
Jay A. Siegel, Pekka J. Saukko, Geoffrey C. Knupfer, Fundamentals of Forensic Science, U.K., 2000.
Stuart H. James, William G Eckert, Interpretation of Bloodstain Evidence at Crime Scene, Washington D.C., 1999.
October 18, 2020 - BY SIFS India