As technology has advanced, forensic scientists have developed methods capable (under the highly controlled environment) of identifying the age, gender, and race of an individual through latent fingerprint analysis.
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Such developments have also allowed scientists to determine the presence of certain contaminants, such as drugs, cosmetics, and food particles, on fingerprints. This progress has also led researchers to discover significant chemical differences that exist between the latent fingerprints of adults and children.
An overview of fingerprints
As one of the most crucial components of any criminal investigation, the collection and examination of fingerprints is the most common type of forensic evidence used around the world.
The three different types of fingerprints include latent, which are invisible to the naked eye unless enhanced by some type of chemical process, visible, such as an inked fingerprint on paper, and molded, which is an indented print found in a thick medium like blood or cement.
Developing latent fingerprints
Since latent fingerprints are otherwise invisible to the naked eye, they require some type of development to be visible for photography and identification.
Typically, a metallic powder, such as aluminum, gold or red bronze, is lightly brushed over a latent-bearing surface to allow for any grease or moisture within the ridges of the fingerprint to emerge visibly.
Once the fingerprint is visualized, it must be carefully lifted onto a transparent lifting tape that is subsequently pressed onto a surface and peeled off.
At this point, the latent fingerprint can be photographed and/or stored for future use.
For many years, criminal investigators were faced with the difficulty of obtaining fingerprint evidence of children, despite mounting evidence that supported the claim that these young victims were present at the scene of the crime.
For example, in 1993, Art Bohanan, a criminologist of the Knoxville Police Department in Tennessee, was unable to obtain the fingerprints of an abducted child from the criminal’s vehicle, which numerous witnesses confirmed seeing the child being pulled into.
However, when a second child abduction case was presented to Mr. Bohanan, he and his team were successfully able to collect the victim’s fingerprints.
As compared to the first case, in which the criminal’s vehicle was not found for four days, the vehicle in the second case was found after seven hours.
Normally, in adult criminal cases, four days should not present any difficulty in fingerprint evidence collection.
Bohanan then concluded that some type of chemical difference existed between the fingerprints of adults and children to prevent this evidence from remaining at the scene of the crime for extended periods.
Comparing the longevity of latent prints
One of the earliest hypotheses to this controversy regarding the rapid evaporation of children’s latent fingerprints was that the secretions of children are higher in volatile fatty acid levels as compared to that of adults.
Since fatty acids are associated with a more rapid evaporation rate, this belief was held as true, despite warranting further research for confirmation.
To this end, a 2001 controlled study compared the fingerprints of children between the ages of 2 and 10 to adults between the ages of 24 and 54.
Herein, all test subjects placed four dry fingers onto a clean glass slide. The fingerprints of all test subjects were lifted on days 1, 3, 5 and 7 through standard latent fingerprint collection techniques.
On day 1, all 47 adult and 50 child participants had clear latent fingerprints; however, on day 3 and 5 of the study, whereas all adult prints could still be lifted, 80% and 54% of the children’s prints were clear on these days, respectively.
On day 7, approximately 91% of the adult prints remained visible, whereas 76% of the children’s prints were no longer clear or complete.
Resolving the controversy with FTIRM
Despite these remarkable findings, little research has been done since this 2001 study to fully elucidate the chemical differences that could exist between the latent fingerprints of children and adults.
This remained true until 2011 when a group of researchers at Brookhaven’s National Synchrotron Light Source (NSLS) applied Fourier transform infrared microspectroscopy (FTIRM) to this endeavor.
FTIRM is a noninvasive and quantitative analytical technique that has previously been used to examine fingerprint composition on various surfaces.
In their work, six adult males between the ages of 35 and 45 years old, as well as their sons, who were between the ages of 7 and 10 years old, provided their fingerprints by first touching their face and then placing the same finger onto an infrared-reflective (MirrIR) glass microscope slide.
This process was repeated 10 times for 4 weeks. FTIRM was used to identify 3-5 skin particles and 3-5 sebum droplets on each collected fingerprint to determine whether any changes occurred during the study.
Chemical profile of fingerprints: Adults vs Children
In general, latent fingerprints are primarily comprised of sebum, which has a composition of approximately 30% free fatty acids, 33% glycerides, 22% wax esters, 10% squalene and 5% cholesterols and hydrocarbons. Until puberty, children will typically produce less sebum-related compounds compared to adults.
This reduced sebum concentration was found to play a key role in why the latent fingerprints of children are less capable of adhering to the metallic powder used during fingerprint collection.
More specifically, hierarchical cluster analysis (HCA) found that there was a significant difference between the lipid and carbonyl ester spectral regions of adult fingerprints as compared to that of the child subjects.
Further investigation determined that the sebum of the adult subjects consisted of more highly branched lipids such as squalene, wax esters and branched fatty acids. The increased presence of these highly branched lipids also meant that a higher fraction of methyl (CH3) groups were present as compared to ethyl (CH2) groups.
The sebum of the children’s samples instead exhibited higher concentrations of long-chain fatty acids, cholesterol and cholesteryl esters, thereby indicating that these samples had a higher concentration of CH2 groups than CH3 groups. Another notable difference between the children’s prints included a higher concentration of cholesterol.
- Cadd, S., Islam, M., Manson, P., & Bleay, S. (2015). Fingerprint composition and aging: A literature review. Science and Justice 55(4); 219-238. DOI: 10.1016/j.scijus.2015.02.004.
- Vanished into thin air: The Search for Children’s Fingerprints. (1995). Analytical Chemistry 67(13); 435A-438A. DOI: 10.1021/ac00109a722.
- Blasdell, R. (2001). The longevity of the latent fingerprints of children vs adults. Policing: An International Journal 24(3); 363-370. DOI: 10.1108/13639510110401726.
- Antoine, K. M., Mortazavi, S., Miller, A. D., & Miller, L. M. (2010). Chemical Differences Are Observed in Children’s Versus Adults’ Latent Fingerprints as a Function of Time. Journal of Forensic Sciences 55(2). DOI: 10.1111/j.1556-4029.2009.01262.x.