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From driver's licenses to smartphone security, fingerprints play a crucial role in identification, but how long do they remain viable post-mortem? Bettmann/Getty ImagesMain Points
- Even after death, fingerprints can serve as a means of identification, though the loss of electrical charge prevents them from unlocking devices such as phones.
- Over time, the accuracy of fingerprint identification diminishes, indicating that fingertip ridges may undergo slight changes during a person's lifetime.
- Sophisticated methods can restore finger tension and volume, enabling the collection of usable fingerprints from bodies in different decomposition stages.
Fans of the Amazon Prime series "Bosch" might recall the chilling season 4 moment where LAPD detective Harry Bosch attempts to unlock a murder victim's phone by pressing the deceased's thumb against the screen, hoping to find crucial clues.
While the show portrays this method as flawless, real-life scenarios, such as a case highlighted in a Tampa Bay Times article, reveal it's far from straightforward. Dead tissue loses its electrical charge, rendering it ineffective for activating a phone's fingerprint sensor and thus, unlocking it.
This raises intriguing questions: Do fingerprints alter post-death, and how long can they be used for identification purposes after someone passes away?
Crime fiction enthusiasts often assume fingerprints remain unchanged over time. However, a study in the July 14, 2015, Proceedings of the National Academy of Sciences indicates that fingerprint identification reliability decreases as the time between prints increases, hinting that fingertip ridges might slightly evolve throughout a person's life.
Despite this, fingerprint identification remains largely reliable for the living or recently deceased with well-preserved bodies. For the deceased, this might involve straightening rigor mortis-stiffened fingers and employing a specialized curved tool to capture prints without rolling the fingertips, as detailed in a book chapter from the National Criminal Justice Reference Service's website.
As outlined in the primer above, identifying a decomposed, desiccated, or water-soaked corpse becomes significantly more challenging. However, it's not entirely out of reach. Medical examiners can excise the hands or fingers of the deceased and send them to a lab for advanced techniques. For severely degraded skin, silicone putty can create a cast of the fingerprint ridges, which can then be photographed and used for identification.
Researchers have made remarkable strides in this field. A study published on November 5, 2013, in GMS Interdisciplinary Plastic and Reconstructive Surgery DGPW explored thanatopractical processing, a method where fluids from other body parts are used to restore finger volume and tension for printing. Out of 400 decomposing bodies, usable fingerprints were obtained in about 75% of cases, with an additional 11% yielding prints sufficient to rule out potential matches.
The longevity of usable fingerprints remains understudied. However, a study from December 22, 2016, in IEEE Xplore, highlighted in a 2017 USA Today article, found that biometric data could be extracted from corpses for up to four days in warm conditions and as long as 50 days in colder climates.
As per Apple's website, Touch ID requires a passcode or password for additional verification if it hasn't been used for 48 hours, ensuring enhanced security for unlocking devices.
