Bloodstain Pattern Analysis In Criminal Investigation

Bloodstain pattern analysis (BPA) or blood spatter is a specialty in the field of forensic science that interprets bloodstains at a crime scene in order to recreate the actions that caused them. The analyst use the location and distribution, along with the size and shape of the bloodstains to form a perspective about what could of happened and what could have not happened at the crime scene. BPA further helps the investigators in figuring out where the events occurred and what time and order they happened in. As well as, who was there and if they were in relation to each other. It may even help the investigators decide between whether the crime was a homicide, accident, or suicide (“A Simplified Guide To Bloodstain Pattern Analysis”, 2015).

By reconstructing the crime scene using bloodstains (blood spatter), the investigators can learn many useful things to aid in their investigation. They can learn what weapons were used and the location, type, and number of wounds caused by that the weapon. Whether the victim defended or tried to escape the perpetrator, if the victim’s body was moved when deceased, and if the victim experienced postmortem violence (Swanson,

2012). For example, a victim was brought into a medical examiner’s office and he/she determines that the victim died from blunt force trauma. The volume of blood and pattern should be in line with an instrument that can cause blunt force trauma by striking the victim multiple times on the head (“A Simplified Guide To Bloodstain Pattern Analysis”, 2015).
Blood is a colloidal fluid, so it will react to outside forces in a foreseeable way. Having said this, bloodstain patterns are highly consistent and can help investigators learn useful facts while reconstructing a crime scene (Bevel, 2002). Some of these facts include: which direction the blood droplets were traveling when landing on a surface, the angle of the droplets when they made impact, the distance from the source to the surface of the blood, the weapon used and how many blows were applied, the locations of other people, the events and when they happened, etc. (Swanson, 2012).
There are many ways blood can leave the body along with the type of injury given. The blood may drip, gush, ooze, or even spray from the wounds leaving different types of spatter patterns. When a source of blood collides with an object it is called impact spatter. When it’s projected out and away from the source it is called forward spatter. When the blood is projected backward from the source it is known as back spatter. Investigators use the speed of the droplet size to classify these impact patterns. This gives the investigators understanding of the general makeup of a crime. Low, medium, and high velocity spatter are the classifications used when determining the impact patterns. Including impact spatter, cast-off and arterial spray spatter are the other sources of blood spatter (Saferstein, 2014). When blood is dispersed from an object in motion covered in blood it is a cast off bloodstain. The arterial spray is exactly what it sounds like. When an artery is cut, the blood exits in either a gushing or spurting manner. In result, bloodstain patterns are usually larger in size (Bevel, 2002). Also, during an investigation of a crime scene, a contact/transfer pattern may appear. An object creates this pattern with blood on it coming into contact with something that does not have blood on it (Saferstein, 2014).
So, why are the bloodstain patterns so important to figure out to the crime scene investigator?

The crime scene investigators analyzing the patterns made by the blood can help in determining the series of events that occurred during the crime scene. In knowing what type of events occurred, the investigators could compare witness statements or rule out any potential suspects. Another thing that the investigators should know about is void patterns. Void patterns happen when a person or object blocks the path of blood. With the void pattern, the investigators can determine if an object is missing from the scene or if there was a person(s) in that particular spot at the time of the incident. It also can tell the investigator if a body was moved (“A Simplified Guide To Bloodstain Pattern Analysis”,

2015).
To be able to reconstruct the crime scene and determine patterns the investigators need to locate blood evidence. Good thing bloodstains are almost limitless in homicides, suicides, and other violent acts. If the crime occurred indoors, then blood will more than likely be found on the floor, walls, and ceiling. If it was a homicide, then the perpetrator will most likely try and get rid of the blood on their hands by wiping them on any type of fabric in the household. If the fabric is dark, the investigator may miss it. Shoeprints may appear on all different types of surfaces and this type of evidence is important because the evidence may link the suspect to the crime.
If the perpetrator tried to clean up the blood there is another way the investigators can locate the evidence. With the use of particular tests such as presumptive or preliminary field tests an investigator can find blood. A water-based spray that locates trace amounts of blood within 30 seconds is called Luminol. Luminol creates a blue glow when the lights are turned off, but it short lasting and cannot tell the difference between animal and human blood. Along with Luminol, hemident also locates the presence of blood, but produces a dark blue/green color in seconds. A type of test that does distinguish between human and animal blood is the hexagon OBTI and usually gives the results in two to three minutes. However, to be able to use the blood evidence in court it must be confirmed by testing done in the laboratory (Swanson, 2012).
The most important thing the investigator needs to do, besides assisting someone that needs medical assistance is to properly document bloodstain evidence. Without, the bloodstain evidence, there can be no bloodstain pattern analysis. The investigator should take notes, photographs, and video recordings of the blood evidence before handling it. A grid or perimeter ruler method can be done to document the bloodstain patterns. Also, the investigator should take note on what the temperature and humidity is and whether the scene suggests the victim was moved if their wounds are severe and no blood exists (Swanson, 2012). In addition, the collection of actually samples of the blood vary depending on what type of surface it is on and if it’s wet or dry. Use a clean cotton cloth with distilled water to moisten the cloth to absorb fresh blood and let it dry naturally. The cotton cloth should then be put in an envelope or clean paper with no openings and proper documentation. If the blood evidence is on an object and clothing, it should be left to air dry and placed in between clean paper. Smaller objects should be done the same way, however if the object is larger and cannot be moved, use a swab or cotton to collect evidence or cut a piece of the object if possible (Saferstein, 2014).
Blood spatter analysis is a very interesting and important job. Since blood is one of the most frequent types of physical evidence that crime scene investigators encounter, blood spatter analysts are in high demand. Crime scene investigation would not be the same today without the careful study of BPA. We would not be able to tell what happened at a crime scene or even tell how many people were involved. The Saint Leo core value of integrity plays an important role in blood spatter analysis in crime scene investigations. The analysts conducting the investigation of the crime should have and use their integrity while trying to figure out what happened. The community is counting on them to be honest, just, and consistent with their work to help find the perpetrator. The findings from the BPA should be honest and never be altered for personal gain. The integrity of the crime scene investigators is very important to us and they should be proud in what they do.