A 3D-printed finger might unlock a phone and solve a murder mystery

Staff and students at Michigan State University are using an unlikely technique to try and help police solve a murder case: a 3D-printed finger.

The team, lead by Department of Computer Science & Engineering professor Anil Jain, has been working on models of a deceased victim's digits to try and help a local force unlock a phone. 

They're hoping the contents of the device will help them unravel the mystery of how that person died.

The project, initially reported by Fusion, has been ongoing for some weeks, Jain told Mashable.

A Michigan police department — Jain wouldn't say which one as the investigation is ongoing — approached him last month after seeing a YouTube video demonstrating his work exposing the security flaws around fingerprint recognition on phones.

In the clip, he demonstrates how fingerprints can be scanned and printed with conductive ink to unlock the devices.

Their work, which focussed on Samsung and Huawei phones, was alsopublished in a paper in February.

In this case, the police "needed to unlock the phone of a murder victim to identify the killer or the suspect," Jain told Mashable. The officers had the person's fingerprints on file but the conductive paper technique wouldn't work on the device, which was a Samsung Galaxy S6.

Fingerprint scanners have advanced considerably since they were first introduced, with early optical scanners replaced by sophisticated capacitive scanners that use tiny capacitor circuits to collect data about a fingerprint. The ridges of a finger are vital to a successful reading.

Jain's team had to use a variety of expensive printing machines to first create a 3D model of the victim's digits and then apply the conductive material to that model. The 3D print had to be a really fine resolution, Jain says, because the space between ridges that the phone's capacitative scanners read is so tiny.

The machines, which cost hundreds of thousands of dollars, are shared with other users and researchers so the project will take several more weeks to complete. The team is experimenting with different types of conductive materials.

"In the next few weeks we will print all ten fingers and then we will see," Jain says. "There's no guarantee it will work."

The use of a person's finger — 3D-copied or otherwise — to access a phone throws up plenty of security and privacy questions. Could, or should, a living suspect's fingerprints be used to access a phone, for example? 

Bryan Choi, an expert on cyberlaw from Penn Law, told Fusion that that could be a possibility. 

“Courts generally draw a line between the ‘contents of the mind’ (which is protected) and ‘tangible’ bodily evidence like blood, DNA, and fingerprints (which is not),” he said. A Virginia court, meanwhile, ruled in 2014 that suspects can be required to unlock their phone with a fingerprint, adding that biometric information is considered outside the protection of the Fifth Amendment.

The University of Michigan team wouldn't be able to use their technique on an iPhone, however — the devices require a passcode if you haven't unlocked it with a fingerprint within eight hours.