Blood plays a crucial role in crime scene investigations, providing vital information and aiding law enforcement in solving cases. A thorough examination of blood found at the crime scene can reveal valuable insights during a police investigation. Some key aspects of blood that are helpful in criminal investigations include the identification of individuals, determination of the cause and manner of death, estimation of the timeline of events, and reconstruction of movements and interactions.

Identification of Individuals: Through DNA analysis, blood can be used to identify victims, suspects, and potential witnesses. By comparing DNA extracted from blood samples found at the crime scene to DNA databases or samples taken from individuals involved in the case, authorities can establish connections and identities of those involved in the crime.

Cause and Manner of Death: The patterns and distribution of blood can provide clues about how a person died. For instance, the presence of arterial spurts may suggest sharp force trauma, while pooling of blood could indicate prolonged bleeding. Blood spatter analysis can also help identify the type of weapon used, the direction and force of the blows, and the sequence of events leading to the victim's death.

Timeline of Events: The condition of blood at the crime scene, such as its freshness or coagulation status, can offer insights into the timeline of events. By analysing the stages of blood clotting and degradation, investigators can estimate the approximate time when the crime occurred. This information can be useful in establishing alibis and corroborating witness statements.

Movement and Interaction: Bloodstain patterns can reveal the movements and interactions of individuals within the crime scene. Transfer stains, swipe marks, and spatter patterns can indicate how blood was deposited, moved, or manipulated during the commission of the crime. By analysing these patterns, investigators can reconstruct the sequence of events and determine the roles of different individuals involved.

A transfer stain, also referred to as a contact stain, refers to a type of bloodstain pattern that appears when a surface comes into contact with an object or surface containing blood and leaves behind a traceable outline or pattern, which is recognizable by its shape, texture, or pattern. These marks are caused when an item or body part carrying blood comes into contact with another item or surface, leaving behind traces of blood. Consequently, transfer stains can provide essential details to investigators about the lifestyles, actions, and interactions of humans at the crime scene.

Notwithstanding, some of the major subtypes include contact stains, impact stains, swipe stains, and transfer stains, all of which have particular features as well as forensic importance.

Swipe Stains: Swipe stains are generated when a blood-carrying object, with its activity over a surface, causes linear or curved patterns. The directionality and shape of swipe stains may be indicative of the movement of an object and can assist in recreating the order of events surrounding a crime.

One can consider wipe stains as those that are left after a blood-bearing item is applied to a surface and then shifted along it, making the blood cover more space. The way wipe stains appear usually depends on the type of material and its porousness.

Transfer patterns: Transfer patterns are defined by the transfer of specific patterns or textures from a blood carrier to any surface. Such evidence may include bloodstains on textiles or even imprints of shoes and tools that have come into contact with surfaces like clothing, flooring, or walls.

Stains from Imprints: Imprint stains are formed when an object stained with blood is pressed onto a surface with sufficient force to create a well-defined print. The print can help in determining the shape, size, and surface texture of the object, which might be useful for identifying weapons or items of clothing used in the crime.

Patterned transfers are those instances when a blood-bearing object, with a pattern or texture on it, leaves an impression on another surface. This could be the shoe sole pattern, tire tread design, or even the fabric weave left on a bloodstained area.

The bloodstains found at the crime scene can be analysed by forensic experts to make a very precise and logical reconstruction of all the actions taken before and during the incident. Moreover, with the help of such an analysis, it is also possible to find out which weapon or object was possibly used in committing the crime, establish how both perpetrators and victims moved around the place where the crime occurred, as well as determine if other people were present at that time. In this manner, transfer stains can be highly useful corroborative evidence in criminal investigations, contributing to supporting witness testimony or suspect's statements and establishing beyond a reasonable doubt a chronological order of events.

Identifying Weapons: Valuable forensic evidence can be obtained from bloodstains found on weapons or objects used in the commission of a crime. By studying blood spatter patterns, DNA profiles, and other characteristics, experts in forensics can connect specific weapons to injuries sustained by victims, potentially identifying murder weapons or tools used in assaults.

Understanding Victim Behaviour: Bloodstains on clothing, furniture, or other surfaces can provide insight into the behaviour and movements of the victim before and during the crime. Defensive wounds, blood trails, and patterns of blood distribution can help reconstruct the victim's actions, including attempts to defend themselves, escape, or seek help.

Discovering Secondary Crime Scenes: Blood evidence may extend beyond the primary crime scene, leading investigators to secondary locations where additional evidence or victims may be found. By following blood trails or examining bloodstained items found in different locations, law enforcement can gather crucial information about the perpetrator's movements and actions.

Identifying Multiple Contributors: Blood mixtures containing DNA from multiple individuals can indicate interactions or altercations involving more than one person. Through DNA analysis and interpretation, forensic experts can determine major and minor contributors to bloodstains, helping investigators differentiate between victims, suspects, and other individuals present at the scene.

Reconstructing the Crime: Bloodstain pattern analysis is a crucial tool in forensic reconstruction, allowing investigators to piece together the events leading up to a crime. By studying the size, shape, distribution, and characteristics of bloodstains, forensic experts can recreate the dynamics of violent encounters, gunshot incidents, or other traumatic events, aiding in the determination of culpability and presenting evidence in court.

Behaviour Profiling: Behavioural profiling utilizes blood evidence to gain insights into a perpetrator's actions, motivations, and psychological state. The manner in which blood is found, handled, or concealed can indicate the offender's level of planning, aggression, and intent, aiding criminal profilers in developing profiles and narrowing down potential suspects.

In conclusion, blood evidence is a crucial component in police investigations as it provides valuable information for solving crimes, identifying perpetrators, and securing convictions. By utilizing advanced forensic techniques and technologies, law enforcement agencies can fully utilize the evidentiary value of blood found at crime scenes, ultimately contributing to the pursuit of justice and ensuring public safety.

Limitations of Blood Evidence:
Blood evidence, although a major component of forensic investigations, has limitations and disadvantages. Initially, the interpretation of blood patterns may be subjective and therefore unreliable; the professional level of an analyst can determine the outcome, leading to incongruities and inaccuracies in conclusions reached after examining these patterns. Furthermore, environmental conditions, including rough or smooth surface texture, can affect stain formation, which may interfere with the analysis of bloodstain patterns.

More so, the use of blood samples to obtain DNA can be unreliable due to degradation over time, contamination, or low sample quantity. Also, in some cases where blood is collected from several sources, it might not be easy to identify individuals involved, especially if the DNA in the samples is a combination of various people.

Furthermore, a presence of blood at a crime scene alone does not mean someone is guilty or has any involvement with the crime. This can have innocent explanations; for instance, accidental injury cases or unrelated incidents can also be involved. Lastly, relying on jurors and the media to accept blood evidence as conclusive proof could seriously influence trial outcomes, which could lead to unjust verdicts being handed down in cases.

Based on the information given, even though blood evidence can be an essential part of forensic inquiries by providing useful clues, the manner in which it is interpreted and its reliability may have some limitations that can result from a variety of errors.
Written By: Md.Imran Wahab, IPS, IGP, Provisioning, West Bengal
Email: [email protected], Ph no: 9836576565