What Stain is This?

The problem

When linking stains to crime scenes the natural thought is of blood and gore all over the walls. But much of the evidence is latent, or not easily visible to the naked eye.

With the modern DNA test sensitivity, even a pinprick of blood on a red carpet is potential evidence.  Other bodily fluids, such as saliva and semen are equally important to solving crime. Without the bright color of blood, they are even more difficult to detect.

The crime scene investigators (CSIs) have to find them all so they can be brought to laboratory for testing.

Looking at things in a different way

If you change the angle of the lighting in a photograph it can pick up details that would not be otherwise visible (Staggs, 2014). The same is true when looking for evidence.

Prior to the 1970s most tests were laboratory based. In the 1980s two portable lamps, one developed in Australia and the other in Canada, allowed investigators to bring the light changes to the scene. Initially, they were bulky boxes with a snake-like lamp attached. Developed for identifying fingerprints, they soon reduced the time spent looking for other evidence as well.  With quicker recovery times, the samples are more fresh and easier to test (Dalrymple, 2020).

The most recent version of this alternate light source is the Crime Lite^TM. This powerful investigative tool is the size of a flashlight allowing investigators greater freedom to search for evidence in hard to reach places (Molinari, 2012).

image 1

Once found, testing the potential evidence can begin.

Are they or Aren’t they?

When evidence arrives at the laboratory, the first action is to make sure the stain is what you think it is. This is where presumptive tests come in.

Bloodstain

Tests for blood are based on an oxidative reaction of the heme molecule in the presence of hydrogen peroxide.  Two popular presumptive tests for blood are the Kastle-Meyer Color test (KM) and the Leucomalachite green (LMG). Both of these tests provide a color change, pink and green respectively, even with very dilute solutions.

If, however, you are expecting to send the sample for further testing, such as DNA, this alters the tests used. LMG is known to prevent DNA analysis. (Tobe et al, 2007)

A negative result is taken as proof there is nothing to be found, but false positives are a problem for presumptive tests. Potatoes and horseradish turn pink when tested by KM.  Iron tonic produces a color change reaction, but the giveaway is that the tonic will react before the hydrogen peroxide is added (Carlysle, 2011).

Image 2

Just washing a blood-stained knife will not guarantee a negative result. Not even bleach can interfere with these tests (Creamer et al, 2005). However, Vitamin C is a strong reducing agent and will inhibit the oxidative reaction (Lee et al, 2016).

Without further testing, it is difficult to tell the difference between human and animal blood. Recent advances offer Fourier transform IR spectrophotometry as a solution. There are already portable devices for paint analysis at crime scenes making it a strong possible for rapid differentiation (Pinho, 2020).

Saliva stain

Saliva is another important piece of forensic evidence. It is found in bites, cigarette butts or glass and plastic bottles – anything that has been near a mouth. All but invisible under the naked eye, saliva fluoresces faintly under an alternative light source (Chatterjee, 2019).

Saliva contains α-amylase, an enzyme which digests starches and sugars (Chatterjee, 2019).The first test performed is the presumptive test, the best known of these is the Phadebas test.  A kit contains strips of filter paper with blue-dyed dots of starch on them. α-amylase breaks down the starch, releasing the blue dye which spreads over the paper like an ink blot.

As saliva is swallowed, the α-amylase travels through the digestive tract and into the bowel. Any fecal contamination spoils the test (Noureddine, 2011).

The Phadebas test does not interfere with further investigation in the form of DNA analysis.

Semen stain

The final bodily fluid found at crime scenes that I want to discuss is Semen. Seminal fluid contains Acid Phosphatase (AP) from the prostate gland. Semen fluoresces in blue or yellow under the alternative light source and it dries as a faint, off-white stain. The acid phosphatase test develops a purple color when AP is present. Unfortunately, a number of other bodily secretions also contain AP, including vaginal fluid.

Because of the high chance of false positives,  a confirmatory test is required. A sample is stained and observed under a microscope. For a really fresh stain, both heads and tails are visible as seen in image 3. Older evidence shows the heads only, as sperm deteriorates quickly outside the body (Rackley Olsen, 2011).

Image 3

Some non-bodily fluids give false positives. Coffee has no effect on the method but  camellia-based teas give the purple stain (Venneman et al, 2014). As detergent interferes with the AP test,  CSIs need to get to any clothes before they are washed (Venneman et al, 2014).

Conclusion

Finding evidence is easier if you look at it under a different light. Once collected, presumptive tests should be used to indicate whether or not a substance is present. Further confirmatory tests need to be performed before a definite ‘yes’ can be offered in court.

Do you think you can identify stains? Tack this quiz and find out.

https://www.opinionstage.com/vanessa-knipe/do-you-know-your-splatters

Images

Cover image: from Wikimedia commons https://commons.wikimedia.org/wiki/File:Cloth_strips_with_blood_-_Public_Domain.jpg

Crime lite, image 1: Found on http://www.fosterfreeman.com/index.php/forensic-light-sources/1-crime-liter-82w

Clip Art Vitamin C bottle, image 2: clipart https://creazilla.com/nodes/22296-bottle-of-vitamin-c-clipart

Stained Semen, image 3: found on https://www.zmescience.com/medicine/genetic/separating-sperm-male-female-14082019/

References

References

Carlysle, F. (2011, March 16). Seeing Red – Presumptive Tests for Blood. TheGIST. https://the-gist.org/2011/03/seeing-red-–-presumptive-tests-for-blood/

Chatterjee S. (2019). Saliva as a forensic tool. Journal of forensic dental sciences, 11(1), 1–4. https://doi.org/10.4103/jfo.jfds_69_18

Creamer JI, Quickenden TI, Crichton LB, Robertson P, Ruhayel RA. (2005). Attempted cleaning of bloodstains and its effect on the forensic luminol test. Luminescence. Nov-Dec;20(6):411-3. https://pubmed.ncbi.nlm.nih.gov/15966054/

Dalrymple. B., (2020) Forensic Light Sources: Four Decades of Detection. Evidence Technology Magazine, (July-August). https://www.evidencemagazine.com/index.php?option=com_content&task=view&id=3197&Itemid=49

Lee H, Park MJ, Sun SH, et al. (2016). Ascorbic acid and vitamin C-containing beverages delay the leucomalachite green reaction to detect latent bloodstains. Legal Medicine (Tokyo, Japan). Nov;23:79-85. https://europepmc.org/article/med/27890109

Molinari, M. (2012, August 2). Wonderful Things: Crime Light. Science Museum. https://blog.sciencemuseum.org.uk/wonderful-things-crime-light/

Noureddine, M. (2011). Forensic Tests for Saliva: What you Should Know. Forensic Resources. https://forensicresources.org/2011/forensic-tests-for-saliva-what-you-should-know/

Pinho, B. (2020, December 11). Rapid Test can tell Human from Animal Blood at Crime Scenes. Chemisty World. https://www.chemistryworld.com/news/rapid-test-can-tell-human-from-animal-blood-at-crime-scenes/4012897.article

Rackley Olsen, S. (2011). Forensic Tests for Semen: What you Should Know. Forensic Resources. https://ncforensics.wordpress.com/2011/10/19/forensic-tests-for-semen-what-you-should-know/

Staggs,S., (2014, September 22) Evidence Photography – At the Crime Scene. Crime Scene Investigator Network. https://www.crime-scene-investigator.net/csp-evidence-photography-at-the-crime-scene.html

Tobe, S., Watson, N., and Daéid, N. (2007, February 1). Evaluation of Six Presumptive Tests for Blood, Their Specificity, Sensitivity, and Effect on High Molecular-Weight DNA. Journal of Forensic Sciences.(52) https://www.researchgate.net/publication/6591230_Evaluation_of_Six_Presumptive_Tests_for_Blood_Their_Specificity_Sensitivity_and_Effect_on_High_Molecular-Weight_DNA

Vennemann M, Scott G, Curran L, Bittner F, Tobe SS. (2014). Sensitivity and specificity of presumptive tests for blood, saliva and semen. Forensic Sci Med Pathol. Mar;10(1):69-75. https://pubmed.ncbi.nlm.nih.gov/24443142/