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Searching for Blood: The 3-Step Method

By: Jocelyne Terilli

Blood is often one the most important pieces of evidence an investigator or lab technician can find. Whether at the crime scene or in the crime lab, there’s a three-step method that will help you work efficiently and thoroughly when searching for blood. This 3-step method involves: Search, Identify, and Enhance. Below, each method and the tools that will help you along the way are reviewed.  You will also find important tips to remember when you’re at the scene.

3stepmethodblood

Search:

TIP: When approaching a scene, it’s best to follow the saying: “Look Down, Look Up, Look Around.” Many times, you’ll find evidence in unlikely spots.

When searching for blood, if it’s fresh blood and wet, it will typically be red. As it dries, blood turns to a brown color, sometimes almost black. Blood dries in relation to temperature and humidity. According to a study in the International Journal of Legal Medicine, blood will take about an hour to dry in a room of about 70 degrees Fahrenheit (20 degree Celsius).

Please also note that using UV light won’t make blood fluoresce. This sometimes causes confusion because other bodily fluids, such as semen and saliva, will fluoresce under UV light.  What blood does is absorb.  The most effective alternate light sources (ALS) for viewing and photographing blood are 405nm (peak absorbance by blood) and infrared for photography (>850nm).

To help you in your search, we have the following tools:

  • Luminol, a luminescent presumptive test for the presence of blood
  • Bluestar, a luminescent presumptive test for the presence or absence of blood
  • Aqueous Leuco Crystal Violet, a presumptive test and stain for blood that also enhances the stain for viewing and photography.

Identify

You don’t want to take the time to collect and process evidence that really is dried tomato juice. Whether you’re at the crime scene or in the lab, it’s best to first presumptively identify the unknown substance as blood.

TIP: Remember: “Take the blood to the chemistry, not the chemistry to the blood”. We don’t want to destroy or dilute the DNA by doing a presumptive test on our only sample. Swab your potential blood evidence to get a sample  then test the swab.

There are everal ways to presumptively identify blood and it depends on your scene, preference, and budget:

  • Phenolphthalein (Kastle-Mayer), a reliable presumptive blood test
  • Leuco-Malachite, a highly-sensitive presumptive blood test
  • Immunoassay tests: RSID or Hexagon Obti,  screening tests that will identify blood and also determine if it is human.

Enhance

Once you have swabbed the area for your evidence, you still want to photograph where the blood is in relation to everything else at the scene. You can enhance the blood so it’s easier to photograph and it will show up properly.

TIP: When using a blood enhancement, always use a fixative. This keeps the blood from running and you losing your evidentiary photograph.  

Again, there are several ways to enhance blood and it depends on your scene, preference, and budget:

  • Amido Black, available in powder and liquid form, the most economical but gives no contrast on dark backgrounds
  • Coomassie Blue, enhances latent prints contaminated with blood
  • Hungarian Red, ideal for dark or multi-colored backgrounds
  • Acid Yellow 7, ideal for multicolor or patterned backgrounds due to its fluorescent properties

By using the three-step method when looking for blood,  you can be confident when you’re processing a scene and collect as much evidence as possible.

If you’re looking for more training, please visit sirchie.com/training. Our popular Evidence Collection class covers the Three-Step Method in more detail with hands-on exercises. Our Bloodstain Pattern Documentation class will also help you document pattern analysis. With Sirchie Training, you’ll learn even more tips to help you in your career.

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