Four Field Tests Used to Detect Blood at a Crime Scene

The average human body contains around ten pints of blood. And when a body suffers a wound, it loses blood. Especially when an attack against a person is violent, blood tends to leak and/or spray throughout the crime scene, even into the tiniest cracks and crevices. Therefore, even if the perpetrator attempts to remove all traces of the crime, it is likely that careful and skilled investigators will still be able to find some of the victim's blood somewhere at the crime scene (Ramsland, 2007; Schiro, 2002). At one time, it was only an idea of fiction that investigators could use some type of chemical to determine whether or not a stain found at a crime scene was actually blood. In fact, it was a technique used in one of my favorite novels, A Study in Scarlet by Sir Arthur Conan Doyle, to aid detectives in their investigation. However, such techniques are no longer a fanciful tool of fictional detectives like Sherlock Holmes (Chapter 1, 2004). Nowadays, there are numerous field tests recognized as accepted ways to detect if a substance at the scene of a crime is blood.

Field Test #1: Strong Light

Because field tests that utilize chemicals can potentially damage or even destroy DNA evidence, it is always advisable to use such methods cautiously. It is best for the investigator to first examine the scene carefully with the naked eye to locate areas that may contain blood or substances that appear to be blood. A strong light can help the investigator locate traces of possible blood that are not readily visible to the naked eye under normal lighting. This method can be especially helpful in locating evidence that may be blood when there is strong suspicion that the offender attempted to clean the crime scene. Ultimately, using the naked eye and an intense light will allow the investigator to evaluate if the substance warrants additional testing and what type of field tests should then be used (Ramsland, 2007; Schiro, 2002).

Field Test #2: Luminol

Sometimes, the investigator may conduct a thorough search with a powerful light and still not find evidence of blood, even though he or she has a strong feeling that blood was present at the scene. Although many perpetrators may use all sorts of measures to rid a crime scene of blood, it is nearly impossible to remove all traces of blood. A chemical, luminol, can be sprayed throughout the area to determine if the investigator's suspicion is correct, usually within five seconds. If there is any latent blood present in the darkened room, it will give off a bluish glow when exposed to a fluorescent light. The glow increases in intensity the more blood is present. Despite its immediate results, luminol should not be considered the best choice to detect blood and should be used sparingly. Unfortunately, lunimol has several disadvantages that can be harmful to valuable blood evidence, including that it has the potential to destroy some genetic markers, as well as dilute blood to the point it can no longer provide any useful genetic information. Also, some substances, such as bleach and copper, can cause a false reading, indicating that blood is present when it is not (Jones, 2006; Ramsland, 2007; Schiro, 2002).

Field Test #3: The Kastle-Meyer Color Test

Another field test used to determine if a substance at a crime scene might be blood is the Kastle-Meyer Color Test. This technique utilizes the chemicals phenolphthalein and hydrogen peroxide to determine if a substance is blood. The solution is used on a section of filter paper and if any hemoglobin is present during the test, the paper will turn a pinkish color, signifying that the substance is indeed blood. However, this field test also has its shortcomings and must be used carefully since substances such as horseradish and potatoes can also turn the filter paper pink, giving the investigator as false reading (Jones, 2006; Ramsland, 2007).

Field Test #4: Fluorescein

A fourth valuable field test is fluorescein. This chemical is also capable of detecting latent or old blood, similar to luminol. It is ideal for fine stains or smears found throughout a crime scene. Fluorescein comes in two formulas, one that is alcohol based and the other which is water based. The former is thicker and sticks well to surfaces, making it ideal for testing vertical areas or those that are quite slick. Also, because of this quality, this first formulation is better for uncovering detailed images of bloodstains. The latter formulation, on the other hand, shows up brighter than the other formulation and is normally used to spray large areas. With both formulations, after the solution has been sprayed onto the substance or area suspected to contain blood, a special light and goggles are used to detect any illuminated areas, which appear greenish-white if blood is present. Regrettably, fluorescein is also vulnerable to many of the same things as luminol (e.g., copper and bleach), making it essential that the investigator ensure that none of these substances are present before concluding that the substance is most likely blood. And finally, whole blood cannot be testing using fluorescein unless it is first diluted because it interferes with the fluorescence of this field test (Latent-prints.com, 2002).

Documentation of Field Test Evidence

Just as with any other type of evidence recovered during an investigation, the investigator should ensure that the results of any field tests are captured for future reference and properly documented in the case file. Whenever possible, any evidence that will be subjected to a field test should be photographed and/or videotaped before and after the test. Often, the illuminations during these tests can be captured on film using special filters for the camera. If this is possible, always include a reference item (e.g., a fluorescent ruler) to indicate the size of the evidence, as you would any other piece of evidence. Some tests, however, cannot be documented through film, so it is acceptable to use a printout of the lab results or written and sworn statements from those who witnessed the field tests to verify and record the test results (Colorado Technical University Online, 2006; Jones, 2006; Latent-prints.com, 2002).

Finally, all information that is marked on every piece of evidence during the collection process should appear in the case file, as well (e.g., name of collector, date/time collected, item description, case number, etc.). This should also include a description of any field tests performed on each item, the results, and the methods used by investigators to capture these results. And if any further tests are conducted on these items, similar information should be added to the case file after the test is completed. If proper documentation is closely followed, field tests can be an invaluable resource for detectives throughout the investigation, along with prosecutors when the case finally reaches court (Colorado Technical University Online, 2006; Jones, 2006).

References:

Chapter 1: Understanding the world of forensics. (2004). Retrieved November 9, 2007, from http://media.wiley.com/product_data/excerpt/04/07645558/0764555804.pdf

Colorado Technical University Online (Ed.). (2006). CRJ445 Phase 3 Course Materials. Retrieved November 9, 2007, from CTU Online, Virtual Campus, CRJ445-0704A-01: Crime Scene Analysis Web site: https://campus.ctuonline.edu

Jones, K. (2006, December 30). How to detect fingerprints and blood at a crime scene: Field reagent tests. Retrieved November 9, 2007, from http://www.associatedcontent.com/article/109258/how_to_detect_fingerprints_and_blood.html

Latent-prints.com. (2002, November 19). Serology: Fluorescein detection of latent bloodstains. In Technical procedures. Retrieved November 9, 2007, from http://www.latent-prints.com/fluorescein2.htm

Ramsland, K. (2007). Chapter 2: Serology. In Serology: It's in the blood. Retrieved November 9, 2007, from CourtTV Crime Library, Criminal Mind/Forensics & Investigation Web site: http://www.crimelibrary.com/criminal_mind/forensics/serology/3.html

Schiro, G. (2002, July). Collection and preservation of blood evidence from crime scenes. 4N6, 20(2). Retrieved November 9, 2007, from Iowa Division of the International Association for Identification Web site: http://www.iowaiai.org/July024N6.pdf