Blood Pattern Analysis: What BPA Can and Can’t Tell us About a Crime

Blood Pattern Analysis, simply put, involves the detailed examination of the shapes and sizes of individual bloodstains and the distribution of bloodstains within a pattern. It is based on the principle that blood will act in a predictable manner when subjected to external forces, and as such it is used mostly in the study of violent crimes and homicides. It is invaluable in helping to understand events at a scene and therefore as part of the justice system, but must equally be supported by appropriate skills and experience to ensure the findings are presented correctly and not overstated.

 

What are the main types of blood staining?

Smears or contact

Direct contact with a surface stained with wet blood will result in a contact bloodstain or smear on the recipient surface. Examples of contact bloodstains includes finger, hair, and fabric marks, stepping in blood resulting in a footwear mark and swipes/wipes.

Spots & spatters

Spots or drips of blood can be produced by blood dripping through the air under the influence of gravity. Thus, they are caused when blood travelling through the air lands on the surface of an item.

The application or force of wet blood can cause the blood to break up and form into droplets which can become airborne and can produce spots and/or splashes on the surface(s) upon which they land.  This is called spattered blood. Spattered blood can be produced by a range of forces, from hard impact into wet blood to the passive action of blood dripping into blood. The expiration of blood from the airways through coughing, sneezing or breathing can also form spattered blood patterns.

Stains

Caused when the appearance of blood on an item does not assist in determining whether the blood is airborne or contact.

 

What are the factors that affect the amount of blood spatter?

How much blood spatter occurs is dependent on a range of factors, including:

The wound type, which is dependent on:

• The weapon or ammunition used
• Calibre/bullet design
• Proximity between the assailant and the victim
• Location of the wound

The spatter pattern, which is dependent on:

• The wound type (depending on the factors listed above)
• Number of wounds
• Hair and/or clothing on the victim
• Presence of an exit wound
• Position of the victim

In addition, the scene or clothing can also affect what spatter patterns can be observed. For example, it is easier to see blood patterns on a clean white wall compared to a dark carpet.

 

What can blood pattern analysis tell you in a forensic investigation?

At the Scene

• Position of the victim and offender and/or objects at the time of bloodshed
• Movement of persons and/or objects around a crime scene
• Whether there was a fight or a struggle of any kind
• Possible type of weapon used
• Minimum number of blows, shots, or actions
• Possible offender injuries
• Amount and nature of blood staining on assailant
• Has anyone attempted to clean up after the assault?

On Clothing

• Actions of the individual wearing the clothing
• Position of the individual wearing the clothing when the blood was deposited
• Attempts to clean the clothing and destroy evidence

On Weapons/Objects

• Was the item used as a weapon or was it just present when blood was shed?
• Was the item moved after the blood was deposited?
• Was an attempt made to clean the item?

 

What are the limitations of blood pattern analysis?

BPA does have limitations including the misinterpretation or over interpretation of blood patterns.

The amount and distribution of blood transferred will depend upon several factors, such as the nature of the contact, the duration of the contact, the proximity of the people/objects involved and the amount of blood that was shed.

After an injury occurs, it can take a varying amounts of time for the blood to flow and become available for transfer to the surfaces and people around. This can range from a very short period of time if a severe injury has occurred to an exposed area, to a longer period of time if the injury is smaller or if it is covered, for example by layers of clothing. Any action a person takes to staunch the flow of blood from a wound, such as holding something to the wound, can also prevent blood becoming available for transfer.

An assault involving a single stab, punch or other injury, while potentially resulting in severe blood loss, may often not result in the transfer of blood to a perpetrator. This is because they may have moved away immediately after the assault and prior to blood being available for transfer. An assault involving repeated stabs, blows or prolonged contact is more likely to result in blood transfer.

 

Blood Pattern Analysis Expertise

Forensic Access boasts a world-class team of forensic scientists operating in state-of-the-art facilities. All forensic work is carried out to the highest quality standards.

All defence work is supported by our dedicated Casework Managers who provide end-to-end assistance and coordination. Direct access to our team of scientists helps barristers and solicitors prepare a more effective defence strategy, and all expert witness reports are thoroughly documented and peer reviewed.

To find out more about our forensic services, or for a free consultation and quote, fill-in our online contact form or Tel: 01235 77480.

We’re also proud to be offering comprehensive training on blood pattern awareness from basic to advanced level, providing forensic practitioners of all experience with a broad idea of what to expect in a case involving the presence of blood.

The courses will be delivered by our own highly experienced blood pattern analysis scientists, who are members of the International Association of Bloodstain Pattern Analysts (IABPA) and will be able to provide practical knowledge, experience, and case examples to bring the teaching material to life. To book your place on the upcoming training visit our dedicated Training and Events page or Tel: 01235 77480.