Bloodstain Pattern Analysis 101: Basic Properties of Blood

Bloodstained Knife

Blood is a fascinating liquid to study in relation to forensics.  About 55% of blood is plasma. Plasma is the “liquid” component made up of proteins, salts, acids, and water. Actually a little over 90% of plasma is water. The other 45% of blood is made up of the cellular material (often called the “formed elements”).  There are three types of blood cells; red, white, and platelets. The majority are red blood cells. Interestingly, red blood cells contain no nuclei and therefore have no value for DNA testing.  In fact, when you consider all properties of blood (plasma and cells) only 1% of that material contains DNA; and that material is randomly distributed throughout the blood volume.

Blood is about 4-5 times more viscous (thicker) than water.  Another interesting quality of blood is that it is somewhat adhesive.  You might be thinking “so what?” but there is a reason these characteristics are important to bloodstain analysts. Thick, sticky blood means that it will adhere to other objects. Those objects may transfer a blood pattern to another object. The more this happens, the more we have to analyze.  A suspect with blood on his/her hands may leave bloody finger or palm prints at the crime scene. Blood on their shirt may transfer to the seat of the getaway car. Blood on their shoes may seep into seams and remain there for months. Even if the blood is cleaned up, trace amounts may still exist.

Bloody transfer of ring on T-shirt

If you are writing a homicide scene, you may want to consider how any blood on your suspect might be transferred during or  after the crime.  If they transport a victim in their car will blood leak out onto the floorboards or into the trunk? If the victim is wrapped in something, what will the killer do with those bloodstained wrappings? In that disposal will any of the blood transfer to the suspect, vehicle, or other objects? As long as blood is somewhat “wet” it can transfer to other objects. Remember, even “invisible” trace amounts of blood can be valuable to the forensic analyst.

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About forensics4fiction

Hi there. Thank you for visiting my BLOG for crime writers. I hope you will find it interesting. I would love to hear your questions and thoughts regarding forensics and criminal investigations. I hope that the information here will help answer your questions or ignite your imagination. I am a retired senior criminalist with 15 years of forensic experience. I have served as the president of the Association for Crime Scene Reconstruction, Rocky Mountain Association of Bloodstain Pattern Analysts, and the Rocky Mountain Division of the International Association for Identification. I am triple board certified in forensic related fields and one of only 40 board-certified bloodstain pattern analysts and 80 board-certified footwear examiners worldwide In addition to writing over 60 scientific papers, I have worked as the editor of the Journal of the Association for Crime Scene Reconstruction, been interviewed by and consulted for television, books, magazines, and newspaper articles including documentaries on the Discovery Channel and National Geographic.

Posted on June 21, 2011, in The Crime Scene and tagged , , , , , , , , , , , . Bookmark the permalink. 3 Comments.

  1. Great post! You have my mind in whirlwind on how to proceed with my next book.
    I’m in a critiuqe group and once a week we have to report a gem or something new we discovered. You were, and are it.
    Thanks,
    Neecy

  2. I posted a comment, and don’t see it! Hmmm… there’s a puzzle.
    This is a great post. In my critique class we have to share a gem, and what we’ve learned over the week. I shared your blog and info to the class.
    Thanks for sharing,
    Neecy

    • Thanks Denise, I don’t think comments are posted automatically but to be honest I’m just getting started here so I’ll look into it. I’m happy to hear you like the blog and find it helpful. Tom

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