1. Bloodstain pattern analysis
Forensic Investigations
Bloodstain pattern analysis

2. What is bloodstain pattern analysis?
The bloodstain patterns left by falling, projected or smeared blood can be analysed by trained crime scene investigators.
Careful observation and measurement of the position and shape of bloodstains can give lots of information about the direction of travel, angle of impact and the speed or velocity of the blood droplets.

3. Definition
“Through the examination of bloodstains and bloodstain patterns, in association with knowledge of the underpinning sciences, they provide a determination of the physical events responsible for their deposition.”
RCMP - Royal Canadian Mounted Police

4. Why is it important in forensics?
Bloodstain patterns can be used to prove or refute a suspect’s account of what happened.
The information from the bloodstain patterns can possibly be used to reconstruct a crime.
Bloodstain pattern analysis can tell us the “how” of a crime.

5. Blood
Blood is a fluid that makes up approximately 8% of the weight of a human body.
Females have approximately 4-5 litres while males have between 5-6 litres.
Blood is made up of cells (red blood cells and white blood cells) plus platelets in a yellowish liquid called plasma.
Plasma contains gases (oxygen, carbon dioxide) and molecules such as proteins, fats and carbohydrates (sugars).

6. Properties of blood
Blood has certain properties that can be compared to water.
Water
Blood
Viscosity
1.0 mP·s-1
3-4 mP·s-1
Surface tension
0.073 N·m-1
0.058 N·m-1
Density
1000 kg/m3
1060 kg/m3

7. Surface tension
Surface tension is an upwards force that enables insects such as a water strider to “walk on water”.
Image: Water strider: David Cappaert,

8. Surface tension
Surface tension enables blood droplets to maintain a sphere shape.
Image courtesy UWA PhD research student Mark Reynolds.

9. Traveling blood droplets
When a force is applied to a mass of blood, the blood breaks into droplets.
The droplets fly through the air as “perfect” spheres due to surface tension.
Image used with permission from Tom Bevel & Ross Gardner, June 2006.

10. Stages of impact

11. Stage 1: contact & collapse
Image used with permission from Tom Bevel & Ross Gardner, June 2006.

12. Stage 2: displacement
Image used with permission from Tom Bevel & Ross Gardner, June 2006.

13. Stage 3: dispersion
Image used with permission from Tom Bevel & Ross Gardner, June 2006.

14. Stage 4: retraction
Image used with permission from Tom Bevel & Ross Gardner, June 2006.

15. Height and size of blood drops
A blood droplet released from a 1m height will be smaller than a blood droplet released from a 1.5m height.
This is because the velocity of the blood droplet released from a higher height is greater.

16. Surface and shape of blood drops
Images courtesy DUIT Multimedia: Paul Ricketts.

17. Low impact
Low impact is really blood under the influence of gravity - it just falls.
Image courtesy UWA PhD research student Mark Reynolds.

18. Medium impact
Medium impact occurs when a force such as a bat is applied.
Image courtesy UWA PhD research student Mark Reynolds.

19. High impact - fine mist of droplets
Image courtesy Stuart James, February 2007

20. Angle of impact
Image used with permission from Stuart James, February 2007.

21. Origin of blood
Image used with permission from Tom Bevel & Ross Gardner, June 2006.

22. Reconstructing the crime
With the evidence that is collected, the crime scene investigator attempts to reconstruct the crime.
This involves trying to work out what events happened and the order that they happened.
Image courtesy UWA PhD research student Mark Reynolds.

23. What other things you may need to know to reconstruct a crime
Forensic pathology results - post mortem information
Forensic biology results - eg, DNA
Witness statements
Impressions - fingerprints, shoeprints
Ballistics
Entomology evidence if appropriate

24. References
Bevel, T. & Gardner, R.M Bloodstain Pattern Analysis. With an introduction to crime scene reconstruction. Boca Raton CRC Press LLC.
James S.H., Kish, P.E. & Sutton, T.P Principles of bloodstain pattern analysis : theory and practice. Boca Raton, CRC Press LLC.
Mark Reynolds, PhD Research Student, Centre for Forensic Science The University of Western Australia.
Paul Ricketts, Photographer, DUIT Multimedia, The University of Western Australia.