• Legis Scriptor

Importance of Blood in Criminal Investigation

Authored by - Ashish Nagpal

Keywords - Blood, criminal investigation, forensic tool, CRPC.


Blood is one of the most important biological traces that can be found on any crime scene. Due to the various valuable information, it contains in itself it is then considered to be a very important forensic tool too. Analysis of the various different aspects of the bloodstains can also contribute to the clarification of the circumstances under which some of the violent crimes have been committed. The presence of such crucial information can help to point the criminal investigation in the right direction and help in solving the crime.

This paper talks in detail about the various provisions involved in the administering of Blood in Criminal Investigation and also the importance of blood in the Criminal Investigation.


The analysis of blood can help in the legal determination of the criminal offense which has been committed. This further can lead to a more precise and more appropriate punishment for the perpetrator who is convicted. Although a very important thing is to determine the correct sequence of events during the commission of a violent crime involving blood. Any valuable Information can be obtained from only a single drop of blood by analyzing its Chemical Compounds as well as measurable Morphological characteristics of the resulting bloodstains. Thorough research of bloodstains can provide crucial information about what has truly happened during the commission of a violent crime which resulted in different shapes of blood patterns on various kinds of surfaces. Since it involves a multidisciplinary approach, forensic experts must have particular knowledge in order to be able to interpret the results of bloodstain analysis properly.

Blood Evidence

In forensic sciences most common evidence is blood. Application of blood evidence is finding blood with the genetic marker i.e the ABO blood grouping and also matching with the appropriate DNA grouping too which is quite an essential part for the application of blood evidence in anything.

Blood is a body fluid found in humans and also in animals whose main work is of delivering necessary nutrients such as oxygen to the cell and also in the transportation of various metabolic wastes away from those cells too.

Biological properties of blood:-

1. The normal blood volume in an average human being consists of nearly 8% of the bodyweight of the individual.

2. Plasma is further defined as the fluid portion of the blood.

3. The cellular portion of blood further consists of the RBCs, WBCs, and also the platelets.

Red Blood Cells ( RBCs )

1. They have a life span of 3 months.

2. Mature RBCs do not have nuclei and they further have a lack of nuclear DNA.

3. It further consists of Hemoglobin which is further defined as the protein which is responsible for the transport of Oxygen.

4. An adult Hemoglobin consists of 4 polypeptide chains of 2 alfas and 2 beta chains.

White Blood Cells (WBCs)

1. This is subdivided into - granulocytes, monocytes and also into lymphocytes.

2. It is involved in the defense of the body against the infection.

3. They have nuclei and are the main source of nuclear DNA from the blood.

4. If white Blood cells are not found in the blood which is found at the crime scene than it would be really difficult to further examine it for DNA testing.


1. Thrombocytes play a huge role in the process of blood clotting.

2. They aggregate at the site at any vascular blood vessel injury and further they are red blood cells and they lack nuclei.

There are two types of blood that are found commonly at a crime scene:-

1. Liquid

2. Dried

The blood evidence in a criminal investigation is almost always in the form of dried stains, so it is quite necessary to understand what happens to the blood when it starts to dry up:-

1. The change in the drying of blood happens when it is exposed to the atmosphere

2.Clotting of the blood starts to happen

3. Compels Changes happens in the structure of the blood

4. Cell structure is starting to destroy

5. Bacteria, fungi, heat and light affect the quality of the blood which further decreases on the passing of time

The important thing to note is with the passing of time blood losses all the identifying characteristics color of the blood and it undergoes successive change. There is a principle in forensic sciences too that "with the passing of time, the evidence changes accordingly".

The following factors affect the drying of the bloodstains:-

1. Temperature:- If the temperature of a particular place is too high then the cell will lose it's characteristics fast, the cells tend to disrupt in their functions with the rise in the temperature conditions while if the temperature is low then the process of degradation slows down.

2. Humidity:- In humid conditions blood doesn't get dried up easily and it has an inverse effect on drying up of blood, although with the rise of temperature the bacterial growth and fungus start to multiply faster in humid conditions and the blood loses it's property quickly.

3. Quantity of blood:- The quantity of blood is directly proportional to the drying-up effect of blood; less blood dries up quickly while large quantities of blood take time to dry up, further it depends upon the conditions like the temperature and humidity.

4. Surface bearing stains:- The surface on which the blood is present also plays an important role as to whether it is sand or glass, different surfaces have different tendencies and these surfaces then further affect the conditions for drying up of blood.

5. Atmospheric conditions:- The atmospheric condition here refers to the condition of rain or wind; Wind results in disruption of characteristics of blood and also results in the drying of blood quickly a din conditions of rain it becomes quite difficult to retrieve the characteristics from the blood.

Crime Scene Investigation of Blood

Even after washing a room for visible blood then also some of the blood evidence remains. A compound called Luminol will cause hemoglobin to fluorescence under black light. Various blood visualization-enhancing chemicals are popularizing with Crime Scene Investigators nowadays and the chemical used for this is Luminol too. Although it has various advantages it has several drawbacks too and it should be the last resort for the investigators to use Luminol. The various disadvantages of using Luminol are:-

1. The major problem associated with the use of Luminol is that to perform confirmatory testing the blood should be present in sufficient quantity, If the blood stain is so dilute that it is only visible with the help of luminol, then no further tests can be performed to confirm the presence of blood

2. The substance Luminol gives false reactions. It reacts with the various ions present in the blood and also it can react with various other things which may be present on the surface

3. According to the various studies performed, It is shown that Luminol will cause the loss of several genetic makers

4. Luminol is water-based and it can therefore cause the stain to smear. It could also dilute an already diluted stain which could cause the sample to push to a limit beyond the detection limits of genetics marker analysis.

Therefore before using Luminol, the investigators must resort to other methods for the detection of blood. In the case where the bloodstain is washed up, the investigators can use High-Intensity light to search for any traces of blood as blood stains are not easy to eradicate and it leaves a brown stain when washed up.

Various Problems Encountered in Collection of Sample

Once the investigator realizes the potential of blood evidence as well as the problem areas encountered in documenting, collecting, and preserving this type of evidence, then he or she will be more effective in finding the best bloodstains. The Various problems which are encountered by the investigators are lack of communication i.e which occurs commonly between investigators and the forensic scientists, Poor reference of the sample, Unfamiliarity with the types of bloodstain analysis, lack of knowledge about the proper technique to be used for the collection of sample and the indiscriminate use of Luminol at the crime scene.


Analysis of the morphological aspects of blood has become a very important process during the Criminal investigation of scenes of violent crimes involving blood traces, in particular, the violent crimes but may also include the other types of criminal events where blood is one of the major evidence on the crime scene, such as in case of traffic accidents or any crime relating to the property. After determining whose is it which is done by analyzing all of the measurable characteristics of the bloodstains obtained from the crime scene where it is left, it can be further determined if it is a murder or a suicide or if the injury was deliberate or not. Unfortunately, because of the major predominance of DNA analysis which is a dominating method of analyzing blood traces, Analysis of the morphological aspects of bloodstains in most countries is not very much developed and also not widely used. It is also valuable to stress the importance of further education and specialization of forensic experts as well as all others involved in the crime scene to help and develop the forensic sciences.


1. Blood Evidence: Basics and Patterns, Crime Museum (Oct 2014).

2. B.R. SHARMA, Forensic Science in Criminal Investigation and Trials, Universal Law Publishing (5d ed. 2014).

HENRY C. LEE, Introduction to Forensic Science and Criminalistics, CRC Press (2d ed. 2019).

3. Doug Hanson, Blood Stain Pattern Analysis: Recreating the Scene of Crime, Law Enforcement Technology (Volume:31 Issue:2), Feb 2014.