Estimating the Age of a Fingerprint
Can we know when a killer left his fingerprints on his victim?
My Epiphany
I like murder mysteries and true crime stories. The Spotify podcast My Favorite Murder is at the top of my list. So, one day, probably after I listened to a podcast, I wondered, “Why don’t the police use fingerprints to know when the perp touched the mirror in the dead person’s bathroom?” Doesn’t that seem reasonable? Is this even possible? I thought so, which led me to do some Googling.
I was quickly overloaded. For example, Environmental DNA (eDNA) is sometimes called “human genetic bycatch.” Still, I was encouraged by the following:
Results demonstrated that human eDNA remains detectable for up to 11 days under laboratory conditions…Partial STR (short tandem repeat) profiles could be recovered from environmental water only up to 24 h…These findings demonstrate that sampling human eDNA from aquatic samples can provide reliable human DNA detection within relatively short time windows, assisting law enforcement agencies by providing information about the potential time an individual may have been present in an area or assisting in the detection and location of a body or remains in aquatic environments. — Assessing the use of environmental DNA (eDNA) as a tool in the detection of human DNA in water
I wasn’t the only person thinking about eDNA and human cells as devices capable of answering the question, “When did the bad guy touch a window, a mirror, or a door knob!
My Discovery
Adding to my idea, I learned that a living cell doesn’t just die and decay the moment cells naturally die or mitochondrial damage occurs. It takes a while for a cell to turn to dust. This delay makes determining when the perp touched the bathroom mirror feasible’ish.
The key to learning the when may be in the keratin. This is good news since the kind of cells that may be left behind are mostly keratin.
Keratin is a protein that helps form hair, nails, and your skin’s outer layer (epidermis). It helps support your skin, heal wounds, and keep your nails and hair healthy. There are 54 kinds of keratin in your body.
- [Cleveland Clinic](https://my.clevelandclinic.org/health/body/23204-keratin)
A helpful characteristic of keratin is that it resists decay. That’s the good news. The bad news is that room temperature, humidity, and sunlight affect keratin’s decay rate. Microbial decomposition of keratin in nature provides these insights, and the decay rate can be impacted by the perp’s skin type, diet, health, and hygiene — hygiene!? That’s one more contaminant for me to worry about. Nevertheless, let’s assume there’s some time limit with a reasonably consistent decay rate. Two days? Ten days?
I need more data!
The test would be performed using mass spectrometry to measure the cell’s decay velocity. Some biology labs already have this capability. The when answer would come from a yet-to-be-developed algorithm — more like a swag[1]. Plugging the rate of decay of keratin into this algorithm would produce a day and time when the perp put the fingerprint on the bathroom mirror.
My Disclaimer
We should use fingerprint dating with caution and in conjunction with other evidence. It may be able to provide some limited value about the timing of a crime, but it’s bleeding-edge science 😉.
My Conclusion
I don’t know if I’m ready for people to have the ability to know when I touched something just by measuring the condition of the keratin I leave behind. But if people can figure out how to fly a drone on Mars, I’m sure someone can develop the technique to use fingerprints for more than identification. We will gain the knowledge and expertise to analyze these brush cells (cells left behind when a person brushes against a surface) not just for their pattern and DNA but to know when they are attached to a surface.
— No part of this article was produced by artificial intelligence (AI) —
