Fingerprint recognition phone
Michigan police have approached researchers at Michigan State University to help them crack a murder case by 3D-printing the victim's fingers to unlock his phoneJason Lee/Reuters

Michigan police have recruited a team of researchers at Michigan State University to help them solve a murder case using an unlikely tool – a 3D print of a murder victim's finger. According to Fusion police approached Anil Jain, a computer science professor at the university, who specialises in biometric security and identifiers, to reproduce a 3D model of the murder victim's fingers using scans from a previous arrest.

They believe the phone of the deceased could possibly hold clues to help them identify the murderer. Rather than approaching the phone's manufacturer for help, local law enforcement asked Jain and his PhD student to produce ten plastic fingers using a 3D printer.

"We don't know which finger the suspect used," Jain told Fusion. "We think it's going to be the thumb or index finger – that's what most people use – but we have all ten."

According to Mashable, Michigan police reached out to him in June after they found a YouTube video that featured the researcher demonstrating biometric security flaws involving fingerprint recognition on smartphones using Samsung and Huawei devices.

"Fingerprint is the most popular biometric trait due to the perceived uniqueness and persistence of friction ridge pattern on human fingers," the researchers wrote in a paper published in February. "It has been forecasted that 50% of smartphones sold by 2019 will have an embedded fingerprint sensor. With the introduction of Apple Pay, Samsung Pay and Android Pay, fingerprint recognition on mobile devices is leveraged for more than just for device unlock; it can also be used for secure mobile payment and other transactions."

"Despite growing usage and claimed security of fingerprint recognition for mobile unlock and payment, spoofing attacks on the embedded fingerprint systems have not been investigated in detail."

With many smartphone fingerprint readers relying on capacitive sensors, gaining access to a person's phone using spoofing methods, are not all that simple.

When someone places their digit on a fingerprint reader, the ridges of the finger and slight electrical charge in a person's skin activates the capacitive sensor for the scanner to read and collect data about it. However, once a tissue is dead, it loses its electrical charge and therefore, cannot activate the sensor and since 3D printing plastic is not conductive, it cannot be read by the scanner either.

To solve this issue, the researchers coated the 3D printed fingers with a thin layer of metallic particles, allowing the scanner to read the plastic digits. The 3D-printed fingers are still being developed and will be given to the police in a few weeks after they have been tested, they said.

The FBI's recent attempts earlier in the year to force Apple to unlock an iPhone used by one of the San Bernardino shooters in 2015 sparked a heated debate surrounding smartphone security, privacy and the needs of law enforcement agencies.

Although the phone in question in that case used a passcode and not a fingerprint scanner, using a dead man's 3D-printed fingerprints to access his phone could potentially raise security concerns. However, Bryan Choi, security and law researcher told Fusion that in this case, the smartphone owner is not the suspect or alive to contest law enforcement's methods.

"The Fifth Amendment protects against self-incrimination. Here, the fingerprints are of the deceased victim, not the murder suspect. Obviously, the victim is not at risk of incrimination," Choi said.

However, for living subjects, a legal standard for compelling people to use their fingerprints to unlock phones and provide access to its content in ongoing cases has not been clearly set yet.

In 2014, a Virginia court ruled that law enforcement can compel users to unlock their smartphones using their fingerprints. In April 2016, an LA court issued a search warrant ordering the girlfriend of an alleged Armenian gang member to use her fingerprint to unlock a seized iPhone.