The 3D Printer

Police asked this 3D printing lab to recreate a dead man’s fingers to unlock his phone 

Last month, law enforcement officers showed up at the lab of Anil Jain, a professor at Michigan State University. Jain wasn’t in trouble; the officers wanted his help. Jain is a computer science professor who works on biometric identifiers such as facial recognition programs, fingerprint scanners and tattoo matching; he wants to make them as difficult to hack as possible. But the police were interested in the opposite of this: they wanted his help to unlock a dead man’s phone.

Jain and his PhD student Sunpreet Arora couldn’t share details of the case with me, since it’s an ongoing investigation, but the gist is this: a man was murdered, and the police think there might be clues to who murdered him stored in his phone. But they can’t get access to the phone without his fingerprint or passcode. So instead of asking the company that made the phone to grant them access, they’re going another route: having the Jain lab create a 3D printed replica of the victim’s fingers. With them, they hope to unlock the phone.

 Arora described how this works to me. The police already have a scan of the victim’s fingerprints taken while he was alive (apparently he had been arrested previously). They gave those scans to the lab, and using them Arora has created 3D printed replicas of all ten digits.

 “We don’t know which finger the suspect used,” he told me by phone. “We think it’s going to be the thumb or index finger—that’s what most people use—but we have all ten.” A 3D printed finger alone often can’t unlock a phone these days. Most fingerprint readers used on phones are capacitive, which means they rely on the closing of tiny electrical circuits to work. 

The ridges of your fingers cause some of these circuits to come in contact with each other, generating an image of the fingerprint. Skin is conductive enough to close these circuits, but the normal 3D printing plastic isn’t, so Arora coated the 3D printed fingers in a thin layer of metallic particles so that the fingerprint scanner can read them. It’s not a foolproof method yet. Arora is still refining the technology, and they haven’t yet given the fingers back to the police to try and unlock the victim’s phone. But Arora said that in a few weeks, once he’s tested the fingers enough in the lab, he’ll hand them over. Then the police will try to use 3D printed models of a dead man’s fingers to unlock his phone.