Forensic Potential of Mascara Analysis
Volumizing, Eye-enhancing, Lengthening. And Crime Solving? Mascara as Trace Evidence
Trace evidence collection and analysis is an essential part of crime scene investigation. When properly isolated, characterized and analyzed, these trace particles can place a victim or perpetrator at the scene of the crime or accident—evidence that has proven to be an important clue to solving many cases.
However, investigators tend to stick to the usual suspects when collecting evidence—fingerprints, hair, blood, and fibers—evidence that a clever criminal will try to obscure. When routine trace evidence collection fails to produce any leads, it is often too late to return to the crime scene. Viable evidence has a short life span and becomes compromised if it is not collected right away. As a result, valuable information is lost.
One type of evidence that is often overlooked by both collectors and perpetrators are eyelashes, more specifically, those with mascara. Although eyelashes fall into the category of fiber collection, they are often deemed too insignificant to collect compared to human hair or clothing fibers. This lack of attention results in missed opportunities.
The abundance of trace eyelashes coupled with brand loyalty among mascara users could provide investigators the ability to place a suspect or victim at the scene of the crime by identifying the personal brand of mascara used. When properly collected, extracted and analyzed, mascara becomes another tool in the arsenal of a crime scene investigator.
The Power of Mascara Analysis
To better illustrate the forensic potential of mascara analysis, I created the following hypothetical investigation:
Three leads, suspect A, B, and C, have been identified based on the testimony of witnesses; however, all three suspects claim that they were never present at the crime scene nor had they ever come in contact with the victim. Evidence collected from each suspect’s clothing included blood, hair, and eyelashes. After closer examination, analysts concluded that the blood and hair follicle belonged to each of the suspects. The eyelashes collected were the only piece of evidence left that required closer analysis.
The proximal end (root end), of all three eyelash samples, collected from the suspects clothes, were placed securely onto a piece of white clean room tacky mat leaving the distal end exposed to a glass slide. Using a fine tungsten needle held at a very low angle, mascara was removed by gently rolling the needle along the length of the exposed hair. The needle was then rolled back over a clean glass slide, depositing any mascara. Deposits were then prepared onto a micro potassium bromide crystal for infrared (IR) analysis and covered with a micro cover glass with refractive index liquid n=1.662 for polarized light microscopy (PLM).
Differences observed between each sample using PLM included binding material, optical properties, and birefringence. Differences in wavelength absorbance by IR were also seen.
Eyelash samples from the victim were then collected and analyzed following the same protocol. According to the data, the mascara removed from the victim’s eyelash matched the mascara found on the eyelash collected from Suspect A.
Independent analyses of the three eyelash mascara samples were then compared to the mascara from the victims’ personal mascara tubes and two other store-bought mascara brands. The eyelash mascara samples were given to the IR analyst as knowns, while the three samples from the tubes were given as unknowns. The IR specialist was able to easily match the mascara eyelash sample with the victim’s brand of mascara. This additional analysis was done to further prove that the use of mascara was a valid technique in determining the presence of the suspect at the scene of the crime.
Any experienced crime scene investigator will tell you that it is the sum of the parts that lead to a conclusive determination. The combination of witness testimony, crime scene evidence and thorough investigation is the only way in which to build a strong case.
Although mascara analysis alone is not enough to make a case, it provides an opportunity for investigators to link people to the scene of the crime. Available in three different forms (liquid, cake or cream) with a plethora of options (color, strengthening, volumizing, lengthening, water-proof, etc.), the variety of combinations and brands make for hundreds of different types of mascara, each with its own unique chemical properties. Users typically stick to one brand at a given time; sometimes loyal customers will use a particular mascara for a lifetime. With the proper preparation and analysis, mascara can become a personal identifier.
For more on mascara analysis, see this article in Evidence Technology Magazine.