Overlapping and faint fingerprints can create difficulties in criminal investigations. However, a recent study presents a promising approach that enables the use of chemical residues found in fingerprints for personal profiling.
This innovative research allows for extracting significantly more details from fingerprints as evidence than what is currently possible.
The Department of Forensic Medicine at Aarhus University has conducted a pioneering study that examines fingerprints on gelatin lifters using chemical imaging techniques—marking the first of its kind globally. This advancement could play a vital role in criminal investigations where existing methods simply do not suffice.
Danish law enforcement commonly gathers fingerprints at crime scenes via gelatin lifters. These lifters are preferred over traditional tape as they are more user-friendly and effectively collect prints from delicate surfaces, such as damaged paint or uneven objects like doorknobs.
Once the fingerprints are captured, they are digitally photographed for processing through fingerprint databases. However, conventional photography fails to distinguish overlapping prints, which are frequently encountered at crime scenes. Similarly, very faint impressions become problematic. Consequently, many fingerprints that could aid in investigations are regrettably cast aside.
A fine spray of solvent
The new research from Aarhus University, recently published in the journal Analytical Chemistry, introduces a solution to these challenges.
“We present a technique that could fit seamlessly into the police’s standard procedures. If adopted, it would allow for a greater number of fingerprints from crime scenes to be analyzed both visually and chemically,” states postdoc Kim Frisch, the primary investigator of the study.
This innovative method relies on a technique called Desorption Electrospray Ionization Mass Spectrometry (DESI-MS). It functions by examining the chemical substances in fingerprints according to their mass.
“A very fine spray of solvent, comprising electrically charged methanol droplets, is applied. This process releases and ionizes chemicals present on the fingerprint surface attached to the gelatin lifter. These substances are then introduced to the instrument, where their individual mass is measured,” explains Kim Frisch.
DESI-MS was developed approximately two decades ago for general surface analysis and proved its efficacy in chemical imaging of fingerprints on glass and tape in 2008.
“Now, we demonstrate that this technique can also analyze fingerprints collected on gelatin lifters, commonly utilized by police in numerous countries, including Denmark. This application of analytical chemistry in forensics holds immense potential,” emphasizes the researcher.
Unveiling fingerprints where traditional optical methods fail
Overlapping fingerprints present a major obstacle for investigators, complicating their separation. The study indicates that the new method can effectively differentiate overlapping prints (see Figure 2) and improve the clarity of faint fingerprints where optical imaging falls short.
To date, the technique has been tested on fingerprints collected in controlled lab environments, but researchers are now applying it to prints obtained from actual crime scenes. They have received fingerprints from Denmark’s National Special Crime Unit, and there is great optimism regarding the findings at the Department of Forensic Medicine.
Could we identify gender, age, and eating habits?
The method remains in the development phase, with researchers intensifying their efforts to analyze the chemical makeup of fingerprints.
A fingerprint contains more than just a distinctive pattern; it includes various chemical compounds from the individual who left the imprint. These compounds consist of natural lipids, amino acids, and peptides secreted from the skin. Additionally, fingerprints may carry traces of substances such as nicotine, caffeine, drugs, cosmetic ingredients, and potentially incriminating materials like lubricants from condoms and explosives that may have transferred through contact.
Chemical imaging could eventually be employed for profiling individuals based on the fingerprints they leave behind.
Research teams worldwide are striving to establish methodologies for this purpose, utilizing different techniques alongside those developed at Aarhus University. Literature has noted that fingerprints can indicate whether individuals have ingested or handled drugs like cocaine, cannabis, and ayahuasca.
Efforts are also underway to determine characteristics such as gender, age, and lifestyle factors like diet, medication, and smoking habits through fingerprint analysis. The Department of Forensic Medicine’s ongoing two-and-a-half-year study, supported by the Danish Victims Fund, aims to maximize the data obtainable from fingerprints.
Research aimed at practical implementation
This research is being conducted in collaboration with the National Special Crime Unit of the Danish Police to ensure that findings translate into real-world applications.
Initial results indicate the method could be practically applicable.
“When police gather fingerprints at a crime scene, the gelatin lifters could, in principle, be sent to the Department of Forensic Medicine for sampling. However, the scanning procedure is time-consuming, which limits our ability to analyze numerous samples at once, as is done with blood samples. We foresee this method being utilized in more serious cases, such as murder and rape, in the future,” says Kim Frisch.
