Violent offences leads to the injuries whichare accompanied by the blood flow. The blood flow due to injury may results inthe formation of pattern of blood stains. These patterns gives the extensiveand investigative information related to the actions or activities occurred atthe time of offence. The analysis of blood stain patterns helps in determiningthe direction of blood travelled, the location or position of source of blood,movement during and after bloodshed etc. Analysis of blood stain patternprovides information about how distinct activities/movements and forces impactsthe appearance and formation of the patterns of bloodstains. It is a usefultool in crime scene investigation in forensics. Bloodstain pattern analysis isthe examination and analysis of the distribution pattern, location, directionand shapes of bloodstains. The examination or analysis of bloodstain patternsis mainly useful in providing elucidation of the physical events that gave riseto the origin of blood stain.Adetailed and extensive understanding of a dynamics of blood as well asformation of stain is a necessary prerequisite to the detailing interpretation ofthe spatter patterns as well as individual bloodstains. BPA is a discipline orbranch of forensic science which deals with blood’s physics and recognize thestains of blood present at scene of crime by using recognition of visualpatterns. This method is useful in shedding light on several forensic matterssuch as event’s reconstruction etc. There are various documented descriptionsof shapes of the bloodstains present at a scene of crime that dates back to thepast few centuries. However, major advances in the field of bloodstain patternanalysis was evoked by the Samuel Sheppard case in United States of America. Analysisof Bloodstain pattern is used by police officials, medics and scientistsworldwide. There are two things which are essential in the evaluation of thebloodstains are blood and surface on which stains of blood are observed. IABPAstands for International Association of Bloodstain Pattern Analysts which is amain organisation for the analysts of bloodstain patterns. Several forms ofmemberships are offered by this organization.
What are the uses of Analysis ofBloodstain Patterns?
BPAstands for Bloodstain Pattern Analysis (BPA) which means it is a systematicassessment, evaluation or examination of the visual bloodstain patterns at ascene of crime which depends on physics of fluids. The analysis of bloodstainsdepends on its size, shape, and distribution also. The main focus of this methodis to answer the question that how a blood travelled through a specific spacein order to produce bloodstains on surface.
Theanalysis of bloodstain patterns is important in:
1. Reconstructing the events of anaccident or offence,
2. Statement verification,
3. In cases which consists of doubt ofinvolvement in an offence,
4. Recognition of areas where themovement of perpetrator is high for the purpose of prioritisation of thesamples of DNA,
5. Differentiation or disparity in betweenan accidents and suicide/homicides.
Analysisor examination of Bloodstain patterns is mainly based on the principles ofphysics, as well as medical, chemical and biological knowledge orunderstanding.
What are thecharacteristics of Bloodstain?
Size and Shape:Theshape of the bloodstain represents the direction of travelling of blood and theangle at which the blood falls on the surface. When the blood passively fall ona smooth and horizontal surface, the bloodstain pattern will be round. Thetexture of the striking surface influence the shape as well as size of thebloodstain pattern. Tough, hard or strong non-porous surface generates roundstain patterns whose edges are smooth. But, the soft and porous striking surface generates spatter stains whoseedges are rough. A drop of blood acquires an oscillating sphere’s shape, whenit falls through the air. Blood drops fall because of the gravitational pulland does not split-up in the air/atmosphere. But additional forces, other thangravitational pull are able to break or split the blood drops.
Angle:Onchanging the angle of blood drop impacting a surface, the bloodstain shape willalso change. The pattern of bloodstain formed will be more elliptical, oval orelongated, when the impacting angle is small or more acute.The determination of angle of impact of the blood drop can bedone by measuring the length and width of the bloodstain. The trigonometricrelationship in between the ratio of long axis vs. short axis of a stain ofblood (length vs. short axis) can be determined. When a drop of bloodfalls vertically at a 90-degree angle, a round stain is formed. The blood dropgets elongated on increasing impacting angle and also a tail develops which ispointing towards the direction of travel of blood drop. A drop of blood will benarrower and longer when struck a target surface at 12 degree angle.
Direction:Theshape of bloodstain will demonstrate the travelling direction of blood. Ingeneral, the “tail” also known as “wave castoff” of the stain of blood indicatesits travelling direction. The travelling direction as well as impacting angleare known as the directionality ofpatterns of bloodstain. The bloodstain directionality is helpful in reconstructingthe location of bloodshed. For example: when a drop of blood falls from a smalldistance, the bloodstain formation will be circular or round up to 45 degreeangle. When a blood droplet falls on a surface at a 90 degree, the circularbloodstain will be formed, due to which the length as well as width of thestain of blood will be uniform. The formation of shape of the bloodstain willbe teardrop or elongated, when a drop of blood falls on a surface at less than 90degrees. The bloodstain’s diameter also increases, on increasing the distanceof 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 alsoincreases, when the volume of blood drop increases. A drop of blood falls offon a surface due to the increase in volume to the extent where the blood’sviscosity overcome by the gravitational pull of Earth and break the surfacetension.
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 animportant factor. Some of the blood react and put it in flight, on impartingexternal force on the static blood. Theamount of blood drops put in flight is less, in low velocity events, but thedroplet’s size will be large. On increasing force, the diameter of a drop ofblood 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 distancetravelled by a blood drop through the air is always dependent on the amount offorce exerted to form a drop, air currents and size of the drop of blood. Theamount of drop of blood in flight is low in case of low force/low velocityevents but the size or dimensions of the blood drops will be large. Thediameter of most of the blood drops will be larger than 3mm, but very few ofthem will be less than a diameter of 3mm. So, the distance travelled by theseblood drops from the source of blood will be short. The amount of drops ofblood put to fly and the distance travelled by them from the source of bloodwill increase on increasing the level of velocity or force. On increasing theimpacting force, the blood drop’s diameter will decrease, with most of thetotal drops of blood having diameter of 1mm. the distance of travelling bysmall blood drops is less due to the lack of physical weight for resisting thefriction and air currents, but the energy responsible for forcing them inflight depletes rapidly. Most of the blood drops which are small in size is notable to travel a distance of more than 3 ft. (0.9 m) from the source of blood. Numbersof drops of blood will be put in the flight which are mainly = or <1mm in adiameter, in case the extent or degree of force becomes very high like spattercaused by gunshot. The blood drop’s size will increase, on increasing thedistance of travel from the source of blood.
What are basic principlesof Analysis of Bloodstain Patterns?
What are the classifications of Bloodstains?
Whatare the analysis of bloodstain patterns performed at scene of crime?