Crimebake–Blood Spatter Analysis

Crimebake saved one of the best panels for last. A detective, whose group specializes in blood spatter analysis, walked us through some of what his job entails, including a couple examples of crime scenes and how to examine the blood spatter evidence.  His group examines the crime scene for physical evidence, latent fingerprints, bloodstain patterns and footwear/tire tracks.

Here are some of the highlights of his presentation:

  • During a homicide when it gets down to the actual act, most people do not anticipate what will happen and that is where they make their mistakes
  • Whenever you see teardrop-shaped blood dripping from knife–that is unrealistic. Blood forms a sphere when it pulls away from the knife
  • THE SMALLER THE BLOOD STAIN, THE CLOSER TO THE SOURCE
  • Bloodstain pattern analysis is one component of a crime scene reconstruction
  • Things can mimic things. It is important to make sure an artery was breached on victim before attributing blood on walls to an arterial spurt
  • Many things can affect spatter such as layers of clothes, weight of victim, etc.
  • Blood spatter is like a water balloon, the harder you hit something, the smaller the stain. Smaller drop moves faster than a large one
  • Bloodstains have been studied since the late 1800s but crime scene blood pattern analysis developed in the 1970s
  • Blood is a fluid and the circulatory system is pressurized. When there is a breach of the circulatory system on a live person there will be different results than on a dead person because the pressure has dropped inside the dead person’s circulatory system
  • There is an adhesive quality to blood
  • There are four stages to a drop of blood hitting a surface:
    • Contact
    • Displacement
    • Dispersion
    • Retraction
  • Blood always dries from the outside in
    • The length of time varies depending on the temperature, the humidity, and many other factors
  • Diameter of blood stain increases with the height you drop the blood from
  • The bigger the surface area, the more blood wells up before it breaks away
  • There is a certain height at which terminal velocity will hit
  • Sometimes suspects have wounded hands because their hand slid down knife and this will cause their blood to drip onto victim
  • Skin is a rough surface and gets spatter on it
  • Directionality is important in bloodstains
    • Tail of bloodstain points to where the blood came from
    • Blood travels in parabolic arc
    • Smaller stains go the least distance because of air resistance and gravity
  • Killer tends to forget to wash high and low and leaves blood stains
    • The flow pattern follows the path of least resistance
  • Vacoules are the little air bubbles in blood
  • Castoffs occur when the weapon is pulled back and forth and the blood comes off
  • Tiny amounts of spatter on shoe means the person was close to the scene
  • Gunshot have a back and forward spatter
    • If the bullet doesn’t exit, there is a larger back spatter
  • Diluted blood stains in kitchen and bathroom point to the killer cleaning up when the person may still be alive and calling for help which is considered cruel and unusual punishment
  • Absence of evidence is not the same thing as evidence of absence

A great way to wrap up Crimebake! Thanks to the organizers and everyone who participated in the panels. You made it a conference to remember. 🙂

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2 Responses to Crimebake–Blood Spatter Analysis

  1. berry says:

    And you gave such a terrific summary. Your notes are so detailed. You really take in a lot of knowledge. They should put you on payroll.

    Seriously you really promote these conferences.
    Good luck on the book.

    • Obsessive note taking is a hazard of being a consultant/auditor for many years. LOL. It helps me process the notes to type them up. So many authors give their time at conferences and through organizations, I’m just doing my tiny part by posting my notes. 🙂

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