Forensic Science Techniques of Blood Grouping and Bloodstain Analysis.

Blood evidence is the core of forensic investigation because it often appears at the scenes of violent crimes and may help to provide significant details concerning the events that occurred during a criminal incident. Two large areas in the forensic analysis of blood evidence include blood grouping – determining the type of blood in a sample – and bloodstain analysis – determining the patterns that have been left by blood at a scene. These methods, when used properly, can assist in the reconstruction of the events, recognize victims or suspects and assist in investigation hypotheses.

1. Forensic Science Blood Grouping Techniques.

Blood grouping is the process of establishing the ABO and other antigenic types of blood samples in crime scenes or on the evidence. In the past, absorption-inhibition was one of the early techniques of typing blood using stains and later, absorption-elution was developed to enhance the sensitivity of old or deteriorated samples.

The method of immunocytochemical identification of the antigens of blood groups (A, B, H) on dried bloodstains is one of the classical forensic techniques. Mixed bloodstains, using immunocytochemical techniques in mixed bloodstains (where two sources of blood exist), one can see each group by immunocytochemical techniques of labelled antibodies, through antigen-antibody reactions. The method has proven to be able to differentiate the first deposited blood and therefore has proven to be able to give useful informationono time sequences in cases of stab or contact. 

The other technique commonly used is the absorption-inhibition and absorption-elution methods, which are commonly used in determining blood group antigens in stains on surfaces such as stone and cloth. Such techniques are based on the reactivity of known with dissolved bloodstain extracts, in which the occurrence or lack of agglutination was a sign of certain antigenic groups. They are standard despite the demand for labour, as the biochemical assays are used to type the bloodstains in case DNA profiling is not possible. 

Presumptive chemical testing (e.g., of redox tests with phenolphthalein, such as Kastle Meyer) is frequently added to blood grouping to ascertain the presence of blood prior to making any attempt at typing. These presumptive tests exploit the catalytic properties of haemoglobin and give a quick sign that a blood sample is present; however, this must be confirmed by further tests to demonstrate forensic validity. 

2. Techniques of Bloodstain Analysis.

Bloodstain analysis refers to a set of scientific techniques that are used to explain the physical patterns that blood leaves when it strikes the surfaces in different situations. Together, this field is referred to as the Bloodstain Pattern Analysis (BPA), which enables analysts to obtain a clue about the force, direction, directionality, and positioning of the occurrences that led to the shedding of blood.

• Classification and Interpretation of Patterns.

Classification of stains according to their morphology is one of the steps that form the basis of bloodstain analysis. Stains of blood are typically divided into passive stain (because of gravity), transfer stain (blood transferred by an object) and projected stain (because of force). The knowledge of these categories will assist the forensic experts in understanding the blood deposition mechanics, including the angle of impact and direction of motion.

Even the form and distribution of bloodstains are also important indicators: long or oval shapes indicate an oblique force of impact; round ones normally indicate the force that is almost perpendicular. The observation and measurement of satellite spatter – smaller secondary droplets can assist with the calculations of convergence points and even directionality in crime reconstruction.

• Experimental and Comparative Studies.

Experimental studies: Experimental studies have demonstrated that the properties of patterns (e.g., distance of satellite and spikes formation) vary consistently depending upon height and the type of surface. Such relationships provide analysts with empirical foundations on which to explain the same pattern at actual crime scenes. The surface texture can also be found to be important in such studies: porous materials will give different stain characteristics than non-porous substrates because of the differences in absorption and spreading. 

(Reference: Rajkumari S. Investigation of Stain Patterns from Diverse Blood Samples on Various Surfaces. J Forensic Sci Res. 2024; 8(1): 028-034. Available from: https://dx.doi.org/10.29328/journal.jfsr.1001061)

3. Spectroscopic and Analytical Techniques.

In addition to visual pattern identification, analysis tools have the potential to boost bloodstain reading:

The use of fluorescence spectroscopy facilitates the process of characterising the blood through the identification of endogenous fluorophores in the stain by forensic scientists. It is a non-destructive, quick and sensitive method with opportunities not only to detect blood presence but also to establish the time since deposition (TSD) with respect to the time-dependent variations in the fluorescence.

The other spectroscopic methods, e.g., near-infrared (NIR) or Raman spectroscopy, could be used to distinguish between the elements of bloodstains and to aid in distinguishing between blood and other fluids or surface materials in the initial examination. 

• Quantitative Reconstruction Methods Integration.

The analysis of a blood stain pattern frequently incorporates quantitative methods of analysis. The instruments, such as trigonometric stringing and area convergence calculation, are used in determining the point of origin of the blood droplets, as the instruments provide insights into the source or movement of the droplet during the incident. These mathematical and physical techniques introduce objectivity other than the subjective observation. 

• Significance and Applied Forensics.

When blood evidence is properly used through application of blood grouping techniques and bloodstain analysis, the evidentiary value of such evidence is improved. Blood grouping is still especially important in serology and preliminary identification in cases where DNA profiling is not available, such as when small or degraded stains alone are available. In the meantime, BPA delivers dynamic reconstruction data that is vitally critical and interrelates physical occurrences at a scene to potential victim and suspect behaviour.

These methods usually run concurrently with the DNA analysis and digital record keeping in present-day forensic laboratories in order to offer a multi-modal view of the proof. Using biochemical blood typing and describing bloodstain patterns in detail and spectroscopic analysis, forensic practitioners can build more credible stories of what occurred in the violent incidents.

Conclusion

Blood evidence (discrete stains or patterns left on surfaces) is a layer of information that can be discovered using a variety of techniques in forensic science. Immunocytochemistry or absorption-elution are biochemical blood grouping techniques that can be used to characterise blood types using stains. In the meantime, the bloodstain pattern evidence, which is backed by traditional visual data, as well as state-of-the-art spectroscopic equipment, such as fluorescence spectroscopy, enables reconstructing the events and dynamics at the crime scene. Further development of these techniques, particularly through making them more sensitive, non-destructive, and more closely tied to the quantitative models, will further improve the forensic value of blood evidence in legal investigations.