Take Nothing but Trouble, Leave Nothing but DNA Footprints
- Science Holic
- 1 day ago
- 4 min read
Author: Joshua Payne
Editors: Ethan Tai & Eason Gao
Artist: Helen Gong
In the dead of night, a gloved hand reaches into a pocket, producing a lockpick. Silent and precise, it unlocks the door. The gloved hand returns the pick to the cargo pants pocket and turns the knob without resistance. The intruder enters, moving deftly and quickly. One gloved hand slides open a drawer, rifling through it for cash and tucking the wads deep into his pocket. The other presses against the wall for balance as his shoe skids across the floor. With the cuff of his glove, he wipes a bead of sweat trickling from his brow. The simple gesture seems inconsequential. In doing so, he inadvertently nudges his hood, sending flakes of dandruff drifting onto the bureau. He edges into the bedroom, brushing his glove against the edge of the nightstand as he reaches for the valuable ring on it. Every surface he touches gets a careful wipe with an alcohol wipe. He thinks he's left nothing behind. Little does he know that on every surface he touched that night is a silent microscopic record that witnessed his crime.
The next morning brings the aftermath: the couple discovers the ring and cash are missing. Their call to the police sets an investigation in motion, with a forensic team arriving to photograph the scene, swab drawer handles, the edge of the nightstand, the top of the bureau, and even a faint smear on the wall. There are no fingerprints—but there isn’t a need for one.
Any one of those deposits likely has more than enough traces to perform DNA analysis. According to Lorente et al. (1998), from a single flake of dandruff (about one milligram in weight) forensic labs can extract between 12,000 and 30,000 skin cells’ worth of DNA (72.5 to 183.3 nanograms), depending on the extraction method. Several studies, including Carrara et al. (2023), Francesco Sessa et al. (2023), and Szkuta et al. (2015), show that DNA can easily transfer from an individual’s body to gloves and tools to objects they touch, such as drawer handles, nightstands, door knobs, and even walls. Not only that, but sweating can increase DNA transfer (Tozzo et al., 2022). A study by M van den Berge in 2016 suggests that moisture from sweat enhances the shedding of skin cells, which “can promote DNA transfer” to surfaces they touch. “Progress in DNA profiling techniques has made it possible to detect even the minimum amount of DNA at a crime scene (i.e., a complete DNA profile can be produced using as little as 100 pg of DNA, equivalent to only 15–20 human cells)” (Francesco Sessa et al., 2023).
What makes this level of detection possible is a relatively recent forensic method for analyzing DNA, known as Touch DNA analysis (“Touch DNA” for short). It is called “touch DNA” because it requires tiny amounts of low-quality genetic material deposited through a slight touch of a surface or a casual handling of an object. It is a modern forensic technique that can amplify and analyze the microscopic deposits, allowing investigators to identify individuals from genetic material that would have been undetectable just a few decades ago.
In fact, touch DNA’s sensitivity is so high that researchers have successfully recovered DNA from footprints left in the snow (UCSC PGL, 2020).
Touch DNA has been used to identify suspects in burglaries, assaults, and other cases where there is no visible evidence. It is extremely sensitive; contamination, secondary transfer, or even tertiary transfer can produce inaccuracies that “hinder or even negate the interpretation of DNA evidence, leading to confusing or even wildly inaccurate identifications as to who was actually present at a crime scene or involved in the commission of a crime” (Schmidt, 2024). A “stark example of this problem” is the Phantom of Heilbronn debacle, where the DNA of “a highly prolific serial killer and burglar” called the “Phantom of Heilbronn” that “was found at 40 crime scenes in Germany, France and Austria” turned out to be “an elderly Polish factory worker who unwittingly contaminated the forensic swabs she manufactured” with her DNA, causing investigators to transfer her DNA to the scenes of unrelated crimes (Schmidt, 2024).
Like the infamous “Barefoot Bandit,” who became famous for literally leaving footprints at crime scenes, modern burglars might think gloves and wipes make them invisible. Still, they just leave different ones—invisible microscopic footprints across every surface they touch, evidence no shoe can hide. But for modern forensics, both are witnesses to the same criminal.
Citations:
Carrara, L., Hicks, T., Samie, L., Taroni, F., & Castella, V. (2023). DNA transfer when using gloves in
burglary simulations. Forensic Science International : Genetics, 63, Article 102823.
Houck, M., & Houck, L. (2008, August 8). What is touch DNA? Scientific American.
Lorente, M., Entrala, C., Lorente, J. A., Alvarez, J. C., Villanueva, E., & Budowle, B. (1999).
Dandruff as a potential source of DNA in forensic casework. Journal of Clinical Forensic
Medicine, 6(1), 58–58. https://doi.org/10.1016/S1353-1131(99)90191-8
Pringle, E., et al. (2007). Recovery of DNA from footprints in snow. UCSC Population Genetics Lab.
Schmidt, J. D. (2024, December 15). Touch-transfer DNA remains misunderstood and still poses high
risk of wrongful conviction. Criminal Legal News.
https://www.criminallegalnews.org/news/2024/dec/15/touch-transfer-dna-remains-
Szkuta, B., Harvey, M. L., Ballantyne, K. N., & van Oorschot, R. A. H. (2015). DNA transfer by
examination tools – a risk for forensic casework? Forensic Science International : Genetics, 16,
Tozzo, P., Mazzobel, E., Marcante, B., Delicati, A., & Caenazzo, L. (2022). Touch DNA Sampling
Methods: Efficacy Evaluation and Systematic Review. International Journal of Molecular
Sciences, 23(24), 15541. https://doi.org/10.3390/ijms232415541
Van den Berge, M., Ozcanhan, G., Zijlstra, S., Lindenbergh, A., & Sijen, T. (2016). Prevalence of
human cell material: DNA and RNA profiling of public and private objects and after activity
scenarios. Forensic Science International : Genetics, 21, 81–89.
Van Oorschot, R. A. H., & Jones, M. K. (1997). DNA fingerprints from fingerprints. Nature
(London), 387(6635), 767–767. https://doi.org/10.1038/42838