Bloodstains at a crime scene hold secrets. To the untrained eye, they’re just messy biological hazards, but for law enforcement, they can be forensic gold. Bloodstain pattern analysis (BPA) blends physics, biology, math, various physical sciences, and investigative skill to piece together violent events. If you’re new to policing or forensics, or simply unfamiliar with how BPA can help you investigate violent scenes, this guide breaks down how to read bloodstains—from drips to mists. Backed by science, it’s your starting point to bloodstain pattern analysis, it’s science, and better resolutions to your cases.
Bloodstain pattern analysis can transform chaos into evidence. It can answer key questions: Where was the victim? How was the attack delivered? Did someone move the body? For beginners in law enforcement, understanding this forensic blood evidence can narrow suspects, challenge alibis, and strengthen courtroom cases. Studies, like those in the Journal of Forensic Sciences, show BPA’s reliability when done right by a properly trained analyst, making it a must-know skill for police.
Blood isn’t just a clue—it’s a fluid with unique traits. Made of red and white cells, platelets, and plasma, it’s slightly thicker than water. This viscosity shapes how blood spatters, drips, or splashes when spilled.
When blood exits a wound, it starts clotting. This changes its look over time, a detail officers must note. Research in Forensic Science International shows temperature and humidity affect drying, too. Hot, dry rooms speed it up; cold, damp ones slow it down. For forensic blood evidence, these basics set the stage. They can give you some ideas regarding length of time since the incident, narrowing or expanding the timeline.
Bloodstain analysis hinges largely on physics. When blood flies—whether from a gunshot or a swing of a blood covered bat—it is subject to gravity, velocity, and resistance forces. Here’s how it works for law enforcement.
Gravity pulls blood downward. A drop falling straight onto flat smooth tile forms a generally circular shape. The higher it falls, the bigger the stain—until it hits terminal velocity. Then the shape size does not change much. Measurements can help estimate blood source height.
A bloody hand swiping a wall leaves a pattern. A bloody shoe walking on hardwood flooring, leaves a pattern. These patterns can help define movements within a scene. This could point toward a suspect fleeing or a prolonged mutual combat, or any number of scenarios. These transfer stains can key in reconstructing crime scenes.
The angle of impact matters, too. An elongated stain means it hit at a certain angle. Breaking out your trigonometry textbook from high school will allow you to determine the angle of impact for the stains. This math, validated by the Journal of Forensic Sciences, can provide blood source location information at or near the time of impact.
Bloodstain Pattern Analysis uses patterns to tell the story. The Scientific working Group, Bloodstain Pattern Analysis subcommittee (SWGSTAIN) defines key terms every law enforcement or legal employee should know.
Rough carpet distorts stains; smooth glass preserves them. The American Journal of Forensic Medicine and Pathology stresses documenting surfaces to avoid errors in bloodstain pattern analysis.
Police use simple and advanced tools for forensic blood evidence. Rulers measure stains, while stringing traces spatter back to its area of origin. Software like Hemospat and Faro automate angle math, but hands-on skill remains vital. While technology is vital to providing better quality, a skilled analyst is still essential. Picking up tiny clues, verifying the technological outputs, comparing the scene reconstruction to inculpatory and exculpatory evidence are all critical parts of an investigation that technology has not mastered.
Beginners should focus on sketches and photos—your work starts the evidence chain. Often the first photographs and sketches are the most important. They can provide a view of the scene before any possible changes, alterations, drying, or accidental void additions are introduced. Getting it right in the beginning may make or break a case.
Imagine a kitchen scene: blood pools under a body, projection patterns hit the wall, and cast-off patterns paint the ceiling. The pool says the victim bled out there. If there are no alterations to the pool, you can make an assumption the victim did not move much after they fell there. Projection patterns mean a breached artery or vein under high pressure. The autopsy should confirm an injury consistent with this. Cast-off suggests repeated movement of a blood covered object. The potential math could place the attacker in a specific position. A void by the sink hints at a missing object. This science helps build a solid case. Now the investigators are looking for missing items, they have an idea (which would get further clarification after detailed BPA analysis) of what took place. They might have a murder weapon they are looking for. DNA samples can connect suspects (if they bled themselves during a prolonged combat), to the scene and to certain activities. These would not necessarily be available to the investigator without BPA.
BPA isn’t foolproof. Foot traffic can alter stains. Rain dilutes outdoor scenes. Misread angles skew results. The 2009 National Academy of Sciences report notes BPA lacks strict error rates. However, properly trained BPA analysts lower the error rates considerably from this study, which did not limit participants to highly trained analysts. Pairing analysis with DNA or ballistics can also increase accuracy.
Beginners: document everything, assume little, and call experts when unsure.
Bloodstain pattern analysis empowers officers. It reveals attack dynamics, exposes lies, and wins convictions. A 2015 Forensic Science Review case showed BPA proving a victim was hit from behind, debunking self-defense claims. For new cops, it’s a skill that turns scenes into solutions.
Contact Revelations Training for more information on our BPA I and BPA II class offerings.
The 5 Essential Items to Have On Every Crime Scene
Strangulation is a type of mechanical asphyxia, which can result in death or permanent disability. Non-fatal strangulation is a increasingly recognized form of domestic violence.
Crisis negotiation is a process of communication between law enforcement and an armed, barricaded, or otherwise dangerous subject, in order to effect a peaceful resolution.
The Big Secret to Decreasing Complaints from the Community is training. By ensuring that your officers are properly trained, you can decrease complaints and lawsuits stemming from officer misconduct or errors. Prevention in the form of quality training is key to avoiding these complaints and creating a more positive relationship between the police and the community.
Drones are becoming an increasingly important tool for police and law enforcement agencies across the country. Also known as SUAS (small unmanned aircraft systems), drones can be used for a variety of tasks, including surveillance, search and rescue, and crowd control.
Get discounts on training, free gear and training, news and training announcements.
Get free bi-weekly law enforcement training articles and a discount on your next session. Plus, snag a free guide: “Top 10 Deadly Mistakes of Suspect Interviews.”
Sign up now! 🌟
