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Jul 6, 2020 in Law

Bloodstains and the Crime Scene

The current paper presents the basic information about bloodstain pattern analysis at the crime scene as well as provides a discussion of various issues associated with the process of blood investigation. It discusses different properties of blood including its physical and biological characteristics that allow a bloodstain analyst to define different aspects of the crime. Modern processes of bloodstain investigation take into account various properties of blood deposited at the crime scene starting from its viscosity to the patterns formed by its drops. As a result, a competent bloodstain analyst is capable of defining a significant variety of issues associated with a particular crime. The outcomes of such an analysis are useful for any forensic specialist allowing accurately detecting a suspect, weapons and the course of events at the crime scene.


Criminal investigations use various methods and tools that allow detecting and analyzing the evidence of different crimes. One of such methods is connected with blood presented at the crime scene and it is defined as the bloodstain pattern analysis. This method of forensic investigation is one of the most efficient ways of reconstructing the crime and identifying the course of events and the crime scene. This paper analyzes the historical aspect of modern approach to bloodstain pattern analysis as well as gives the basic characteristics of the aspects that are present at its core. Correctly interpreted patterns of bloodstains at the crime scene allow obtaining the most important information about the crime as well as reconstruct the crime scene in detail. This analysis allows exploring the behavior of the suspects and their victims and identifying the vital evidence that leads to the potential criminal. Therefore, future specialists of forensics have to increase their competence in bloodstain pattern analysis in order to increase the overall productivity of their work.

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Bloodstain pattern analysis (BPA) is a critical procedure at the crime scenes that involves the presence of blood, which is why specialists should consider different safety issues during the procedures of samples collection and their analysis. As any liquid substance, blood has different physical properties some of which are granted by its biological nature. Thus, it may flow and change its shape as well as viscosity, which impacts its surface tension and density. These properties significantly depend on the amount of time since the blood is exposed to the air and is not present at the physical body that maintains its initial state. At the same time, there is a need to state that blood is relatively thick, but definitely thicker than water. However, these properties also depend on the temperature of the environment where cold temperature makes it thicker and high temperature increases its thinness. Furthermore, blood samples tend to sink in water because its relative density is 1.06, which is denser than water. In addition, another important visual property of blood is its sample sizes and their shapes. An average blood drop has a spherical form and tends to preserve because of high visocsity it if not affected by any force and has a size of approximately 0.05 mL. At the same time, it is significant to remember that the unique physical properties of blood are caused by the aspects of its biological structure.

Considering the biological aspects of blood analysis, it is worth noting that blood is not a usual liquid that consists of similar molecules and other components. It has a group of different cells that perform various life-supporting tasks in a living organism, which impacts their properties. Thus, blood components are red blood cells or erythrocytes, white blood cells or leucocytes and plasma. Red blood cells are of critical importance for the BPA analyst because they contain such elements as hemoglobin and iron, the properties of which are important for blood detection. For instance, an expert may use a set of color change reactions that allow detecting iron presented in blood, therefore, exposing the evidence of blood presence. Another critical aspect of red blood cells is their validity for the DNA analysis as they have a nucleus. 

Lastly, it is critical to note that as blood is a biological substance, the process of its collection and analysis requires specific safety interventions. The reason for it is that a victim or a suspect may have an infectious blood-transmitted disease, such as HIV/AIDS, and an analyst may spoil the sample by engaging in an unprotected physical contact with it. Therefore, while being within the crime scene, individuals are exposed to the blood depending on the context of a particular situation within their operations. Consequently, it is important to be aware of the fact that he/she should protect oneself from a possible injection or inhalation of ingestion of bloodstain samples. This aspect is important because they may be located almost at any place at the crime scene such as door handles, the floor, the walls or the ceiling, cups, kitchen counters and other. The protection from the blood at the crime scene can be granted by special gear such as masks, rubber gloves, eye protection and special protective suits. Special attention should be given to open wounds and in the case of contact with blood, there is a need for an urgent disinfection. At the same time, the variety of protection methods depend on a particular crime scene and the selected collection methods. 

Blood Collection and Analysis

Forensic specialists may use different methods of blood collection and analysis, the selection of which depends on the actual situation at the crime scene. For instance, in some cases, it is enough to take a photograph of the surface that contains bloodstains whereas other ones require obtaining blood samples to the laboratory for further analysis. The latter may require taking the part of the surface together with bloodstains in order not to cause any physical influence on the collected blood samples. At the same time, if an analyst takes a photograph, he/she has to follow the guidelines that allow obtaining critical information in the future. Among them is placing a ruler near the bloodstain for supplying it with measurement details and using high-quality devices for obtaining high-resolution photographs that depict stain pattern details. Furthermore, specialists perform BPA that consists of the phases of stain pattern analysis and reconstruction. Both of them require competent specialists in order to adequately interpret the present blood samples.

Blood pattern analysis is the process during which a forensic specialist investigates the physical characteristics of blood, its shape, amount, and distribution at the crime scene. The aim of this process is a comprehensive explanation of the causes that made the blood forming a particular shape and constituency. This phase requires the usage of deduction, which focuses on the available information about particular bloodstains and attempts explaining the course of events at the crime scene, and is followed by the reconstruction. Forensic experts require this phase for synthesizing all the obtained evidence and using it in order to explain the aspects of bloodstain patterns in the context of the actual crime. For instance, this phase may bring the awareness of the used weapon on the basis of the angle of distribution of blood drops, their quantity, and the forces affecting them. Similarly, it is possible to reconstruct the time of the murder on the basis of properties of blood such as viscosity and thickness. Another aspect that is possible to reconstruct is the question of the voluntariness of death, which can lead to the fact of assault, lethal accident or murder. Therefore, BPA provides a great volume of information that is used for investigating the time of crime, its motives, used weaponry, and thus, convict or discharge the suspect.

Bloodstain Types

The competency of bloodstain analyst is assessed depending on one’s awareness and skills of interpreting various bloodstain types and their tests. Despite the classifications of bloodstains may differ, one may divide them into two groups, spatter and non-spatter stains, that are the result of different forces affecting the blood. One may classify spatter stains into drip stains and drip trails, cast-offs, impact patterns and projection spurts. The force that affects drip stains is gravity, which leads to their free fall on different objects and surfaces. The impact of this physical force also leads to the shape of the stain leading to its radiation away from the center causing irregular edges. At the same time, drip trails are accumulated stains that allow tracing the movement of the source of blood drops allowing investigating different directions towards the body or weapons. Cast-off blood patterns are mostly linear and indicate that blood sticks to a particular object and allow determining the type of the weapon and the amount of hits done by the suspect. Projections are big quantities of blood caused by strong arterial blood flow and indicate that an artery of a victim was breached. Impact patterns are a result of hitting liquid blood that causes its radiation apart from the epicenter of the impact. Their analysis allows obtaining data about the initial location of the source of blood that is defined as an area of origin. Furthermore, non-spatter stains are saturation and transfer stains, pools, smears, and blood contacting or mixing blood. Saturation stains are the result of blood absorbing by materials and allow identifying the amount of blood loss or body location. Similarly, transfer stains are patterns, which were caused by an interaction of blood with other objects, and demonstrate the fact of movement within the scene. Moreover, smears may be specific types of transfer stains that indicate on blood wiping or swiping when blood contacts with already deposited blood or a non-blood material. Lastly, there are cases when blood contacts with the blood that had already been present producing a secondary impact. All the identified types of blood should undergo presumptive testing that allows defining or disproving that the substance deposited at the crime scene is blood. For this, experts use different sensitive substances, such as phenolphthalein or tetramethylbenzidine, which change their color indicating towards the nature of the analyzed substance. However, some of them may give false positive result, which requires profound competence of the investigator. Therefore, a skillful bloodstain analyst is capable of defining a lot of factors on the basis of bloodstain patterns presented at the crime scene. Among them, one can name the weapon, the location of the body, the causes of victim’s death and other, which are of critical importance for the participants of a crime investigation process.


Bloodstain pattern analysis is one of the most efficient approaches in the sphere of criminal investigation that gives forensic specialists a lot of critical information about the crime. Among the facts that may be exposed in the result of the analysis is the source of blood, the cause of the crime, the weapon used, the associated events and the crime scene such as movement of the body and other. Moreover, skillful bloodstain pattern analysts are capable of reconstructing the crime, which gives a possibility for convicting or discharging the suspect. Therefore, forensic specialists should enhance their skills in bloodstain analysis for the overall increase of their working efficacy.

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